That one is maybe the easiest to do :

express your gratitude to the maintainers

Besides that there is the possibility to donate. And since the xz backdoor incident I would say it makes sense to keep an eye on end users trying to bully or overload developers. If I remember well I read that the developer of uMatrix stopped with that project because of annoying users filing bug reports with unfriendly and demanding discourse, which can be exhausting for a sole developer.