So, that one developer is the main developer of Lemmy, and you may be surprised to find out there are only two of them. Lemmy is open source and takes contributions from others, but its development is driven by two full time devs.
If you want to donate to development, that's how to do it. If you want to donate to a specific instance to keep it online, then follow any donation instructions in your instance's sidebar.
I'm preemptively defederating from Threads. But I'm not necessarily opposed to refederating in the future, if Meta proves benevolent. Some bigger Mastodon admins are going with a wait and see approach, but as the sole admin of a small instance, I'd rather not have to rush to defederate if shit hits the fan.