Pretty much any functioning laptop will find a buyer if it is capable of running a modern web browser and in many cases there are enthusiasts willing to take hardware that can't even do that.
Over the past couple of years I have sold hundreds of bits of old computers ranging in age from five years old to 25 years old. Everything from ThinkPads to 20 year old power supplies taken from scrapped Compaq desktops and all the components in between including tape drives, DEC terminals, etc.
I also sold a non-functioning Quad 303 power amp for 1000 NOK (112 USD). Could perhaps have got more for it but as it hadn't cost me anything and it had been waiting for repair for over ten years it was a good price.
Someone will want your Mac mini, they just need to be able to find it. Put it on Ebay, Gumtree, Craigslist, Finn.no, or whatever your locality has.
I personally find that Mac hardware holds its utility far beyond its value, and that's even recognizing that most Mac products hold value in the second-hand market.
I saw a Mac Pro 5.1 ( same generation as your mini ) on craigslist recently, refurbished, but selling for four figures.
The last thing I want is to be an accumulator of stuff, so ending up in a cupboard is not an option.
I like the reuse concept (as a general rule I buy refurbished equipment when ever I can) so if you don't need it any longer, maybe someone else would find it useful?
My family's previous retired laptops were 2 old HP Core i3 4th gen models. With 1366x768 15" screens, one of which was cracked. One would blue-screened randomly after a few hours even with a OS reinstall. I stripped them down and sold the motherboard and RAM of the non-blue-screening one on eBay and made about $80.
The rest was recycled because, what would I do with them? If I wanted a Plex server, a Raspberry Pi 4 is powerful enough for most things that don't need transcoding, and consumes far less power and physical space (laptop motherboards are not very space efficient for a server unless you got a super long and thin case for them).
Older desktops -- if not noisy gaming PCs -- become servers or get harvested for parts to bolster an existing one, otherwise they get donated or recycled.
I donate excess computers I don't need anymore that are in serviceable condition to local charities: there are lots of under-served communities that need laptops and routers and modems in this day and age with remote learning during lockdowns, etc.
The rest I try to tear down for useable parts (to keep the frankencloud running) and the rest I recycle as best I can.
2. Retro gaming / retro development, which given the age of something often means C or C++.
3. If things are really broken, e-waste is probably the only option.
I'm using Apple since 2014 and realised I've gathered quite stack of old Macs (one Macbook Air, one MBP and one iMac). I've installed Linux in all of them for the heck of it and its quite a welcome break for macOS.
I try use the old Macbook Air only as a thin client (tiling window manager and most TUI applications for IRC, email, coding, remote admin, etc).
Why El Capitan? Because the most current Chrome requires El Capitan (Mavericks does not work). Actually I use ungoogled-chromium. While it might seem super dangerous to connect to the internet because of security, I took some measures:
On my Router (Fritzbox, but any other quality router will do):
- Isolate that device to "Guest" WiFi so it can only connect to the internet, not other devices in my LAN (works by Mac Address Filtering)
- Do not allow unknown MAC Addresses to connect to WiFi at all for all my home network
- Only allow outgoing ports 80/443 TCP and 53 UDP on the Mac, refuse all incoming connections (its NAT anyway but just to be sure)
- Disable UPnP for that device
When using the device:
- Never use ANY login/private data on that device (see exceptions below)
- Never enter any private data, so no social media, email, iCloud etc. just plain surfing
- I strictly only use AirDrop from my modern Mac or a readonly SDcard to copy files ONTO it (Movies, Music, Ebooks, Podcasts), never download or copy the other way around.
- The only Applications I installed are ungoogled-chromium (plus ublock origin) and VLC
I use it to watch (offline) movies, music podcasts and sometimes Netflix. Additionally I connect my E-Piano with a piano learning website to it over USB (Benefit is I can use GarageBand instrument library with it). For those two websites the passwords are strictly unique. When not in use, I always do a full shutdown (no sleep).
I know that a super-dedicated and driven hacker might - with lots of work - use the device as attack vector, but I mostly think this is a highly unlikely event. Especially since it is way easier to compromise servers with log4shell right now :)
Edit: Btw it is super easy to downgrade, just hold CMD+Option+Shift+R on powerup, and the internet recovery will install the macOS version the device shipped with. Then go to https://support.apple.com/en-us/HT211683 and download the full OS as a simple .pkg file on another machine, copy to SDcard and start installation.
If I have the feeling that someone else might find it useful.
Recycling: If it had sensitive data on it and cleaning it up is not worth it at all like small and old hard drives or old and slow USB stick.
Gifting:
If I have the feeling that it would help. Like a laptop which is old but not too old for normal daily use. I will clean it, fix it and search for someone to gift it.
I do try to do something with those things fast as it only makes it less useful longer I wait.
It also annoys you when it is inconvenient like when you move and find all of the old stuff. Or you lost that space for ages and then you throw it out anyway.
I also have a powerbook that I purchased from ebay but running xcode seems to be too slow so not sure what to do.
It's right next to the wardrobe. Which is pretty useful during the winter in Montreal.
I wouldn't mind giving it, but it's not something people do much here, and I'd rather pay taxes to organize rather than pay some religious charity who would help people only if they give their soul in exchange.
I have thrown very little hardware the last 10 years, because I buy long term, have small desires, don't buy MACs or anything that has to follow some sort of replacement fashion (but that's why my stuff wouldnt have much resell value anyway), or it's hard drive, and I dont dare throwing away hard drives here in China hehehe. I have a full 4x2TB and 4x10TB set of NAS hardrives that I had to keep in store when I moved to 4x18TB (Ultrastar <3), that's probably the only thing I have to find what to do with now.
Video cards, I change when they break, and do throw them away: I'm at my 3rd top-end NVidia, since 2010. Switching from cheap craps to very expensive video cards is probably the biggest source of savings I've ever done hardware-wise. Instead of having a litany of time wasting problems, immediate obsolescence and replacement every year or so, I can just drive the card until it short-circuit and never have to compromise. They do short-circuit at regular interval, interestingly.