Immich and photoprism do AI detection and sorting right? Until they have scanned through all current photos you are going to have a lot of system load. And my 4 gig pi usually jusy runs at 1 gig of memory and low load…no Immich, but running Openmediavault for DAAP and SAMBA, and DejaDup and Syncthing, homeassistant, CUPS, etc.