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 started to donate once a year to my Linux os and apps I like. I also need to set up a small monthly for apps I like. If we don’t show support when we can we will lose the some great projects.