Pop Shop is kinda slow. COSMIC Store is part of Pop OS’s new COSMIC Desktop Environment (DE). Everything is just a lot faster. It’s an alpha so there are a couple of rough edges, but it’s great overall.
Speaking of, get hyped for COSMIC. It’s a DE written in Rust. It’s not quite as complete as GNOME, but hopefully it will have better performance than the current GNOME mod that forms Pop’s UI.