Here are the solutions I've tried:
[1] Safari. Works really well on iOS, and I want it on Android, but isn't available.
[2] Opera claims to have reader mode, but when I tried it it just seems to add its own adverts, along with a "click here to read more" link on all pages. So ultimately it just removes everyone else's adverts and adds their own even worse ads. I get they have to make money, but the whole thing is unusable.
[3] Android Reading Mode. Now, this would be an excellent solution if it actually worked and was thought through, but no, it's a disaster. So you install the "reading mode" app, then turn it on in settings. Now you have a choice: either enable the permanent little annoying bubble that appears all the time, even when reading mode can't be used. Or, choose to click both volume buttons at the same time. The problem with this is that it beeps every time you do that, and the beep cannot be disabled unless you turn "ring & notification volume" to zero. The beep can't be disabled by using "do not disturb", and the "reading mode" app claims it is not using notifications, so there is no way to disable it there. Overall I think google must just have tried to make Reading Mode as annoying as possible so that they can say "hey, we have accessibility", but it's just so annoying that nobody will ever use it.
I haven't found any other solutions to the problem yet.
You may also like SponsorBlock (https://addons.mozilla.org/en-US/firefox/addon/sponsorblock/), though it is not currently available on Android. It lets you skip over advertising inside of videos.
When in reader mode tap the menu icon and select the option to adjust reader mode settings to change font.