Still learning about the fediverse, but… What about a simple percentage system so you can donate whatever you want. A large portion goes to the instance that you register with and smaller portions go to Lemmy programmers. Maybe portions can be set aside for parts of the fediverse that we all use like gif/video hosting. I’d say make the percentages the same across the fediverse so people know what goes where.

Personally I’d prefer monthly giving like patreon.