I’ve got some standing orders of 1 or 2 euros every month for bigger projects like grapheneos and kde. And for small apps that I actively use, I try to donate 5 or 10 euros now and then. It’s not much but I believe if everyone is doing their part we succeed in the long run
I’m donating a shy of 20€ per month to services automatically on Liberapay/Opencollective as long as I can. I do /try/ to give back on the projects that I use a lot in either my time and effort (IE: sitting in their IRC channels helping people for example), or a monetary donation.
It’s not much, and I hope these open source projects never become something that depend on money and donations, but there are always cost to running services online.