Yeah, initial launch always seems to have issues. Same if you come back to the vault after a lot of changes have taken place. iCloud is simply stubborn about how files are handled, and Obsidian needs to see every file in the vault. That initial downloading and indexing activity is what causes the lag, but once it’s done, it tends to perform perfectly.
The only solution I can imagine is deliberately locking down the app while this loading activity takes place, giving the use only a progress bar, loading screen, or similar.