To which projects do you give a little financial support?
[1] https://foundation.mozilla.org/en/blog/fellow-research-decen...
I feel that this can give a considerable boost to someone's motivation, while it is a small drop in the bucket for established organizations and projects. It will not "go to waste" with larger ones, but it will not feel as personal as a (typically) single maintainer getting donations -- which they do get rarely.
Go through your list of browser or mail client extensions, for example!
Arch Linux: I've been a user for 10 years and haven't given back financially.
OpenBSD: Underpins some of the most important tools in the modern FOSS world (OpenSSH, OpenSMTPD, tmux, among others), my website and mail server run on it and it's a joy to use and administer. Essentially no maintenance other than patching and it's so simple that I don't have to worry about being vulnerable.
If your using linux, your using GNU as well.
Related, projects I've donated to in the past are QGIS, a great FOSS alternative to the limited and heinously overpriced ArcMap, and Homebrew, which despite it's ubiquity doesn't bring in the developer much money.
I also chip in toward upkeep on my favorite Mastodon instance.
I still donate to ffmpeg (it's used in more software than you might think), newpipe, signal (the signal foundation, the people behind the end to end encrypted messenger) and debian.
I use all of the above software and I'm fairly happy with it.
OpenStreetMap Wikipedia DAVx5 Jellyfin Mobian Thunderbird PureMaps Sequeler rust-gtk