The next Lemmy version will add a donation dialog, which is shown once a year to every user, in order to increase the amount of donations for Lemmy development. You can see the current text in the screenshot above and in the translations repo. You can also checkout the frontend PR. Is there anything you would change about the text?
Edit: This is how the final design looks like:
I opened an issue regarding a donation dialog for instance admins, which seems closer to what you mean.
https://github.com/LemmyNet/lemmy/issues/5613