Yes, I have a Pi4 2GB, it's still working as a second pi hole node. That's what got me into the world of self-hosting, but 2GB is not enough for a lot of things. I went from that to a N100 with 16GB of RAM, so the difference is huge and I think it's totally worth the money.
I haven't tried Immich, but I probably will once I have a better solution for storage.
Good human