I think people often forget federation is not a new thing, it’s a first design for internet communication services. Email, which is predating the Internet, is also federated network and most popular widely adopted of them all modes of Internet communication. It also had spam issues and there where many solutions for that case.
The one I liked the most was hashcash, since it requires not trust. It’s the first proof-of-work system and it was an inspiration to blockchains.
Using apps that cant provide anonymity and at the same time not the ones that do is very dangerous for society as a whole. Some journalist and activist need anonymity and if only place where they can be heard is on mainstream apps that don’t offer anonymity, they are stuck.
Yes, I write credentials in a file and encrypt them with my public key. Then I use my private key to decrypt them when needed.
I use gpg to encrypt my passwords with my public key. Benefit is that adding credentials to a new file doesn’t require me to type the master password (password for private key). I trust gpg the most for security.
What about pinephone?