It could be done with GNU Taler. There is even some NLnet funded grants for open-source projects to integrate it.

The fediverse app would need to implement a relatively basic frontend and someone would need to host a so called merchant backend that multiple people could share to collect funds.

The main show stopper is the final bank integration, but it looks like there will be some options in the EU at least starting mid of 2025. Basically you will be able to make a SEPA bank transfer to charge your GNU Taler wallet (you can use an open-source mobile app or a browser plugin for that) and then you can use these funds to make payments and donations.