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
When one of my “cloud” devices / services becomes “enshittified”, I’ll donate what the provide is asking to a related open source self-hosted project.
I also “buy” the major update for whatever software I use regularly.