I used to use Yattee + Piped and it was great, until Piped stopped working on iOS devices (I tried all the fixes I found, none seems to work). And I just switched to Yattee + Invidious but it seems to be limited to 360p for me (whereas Invidious works normally elsewhere). But it’s the first time I hear about Yattee-server. What’s the point of it? What does it add to Yattee + Invidious?

I don’t know what up with your Immich instance but this seems like a lot of RAM usage for me. I have 45 docker containers, including Immich, running on a 10 yo NUC with 8 GB of RAM and that’s not an issue… I use 4,7 GB total in this instant.