Sure but I would think Anubis would also somewhat stop DDOS attacks since clients need to pass Anubis to access the website and across a DDOS swarm that would use up significant resources.

Wouldn’t anubis be effective against DDOS attacks?

You can use Immich, it’s not perfect for this use case but it is searchable by content. You could just create a second account so you don’t even need to host an extra service

Nobody using Instagram DM’s is actually going to go out of their way to encrypt messages like that, people who care about privacy are going to move their conversations to Signal or another secure app with E2EE built in