I just installed the Tuta app from the Play store, made a test contact, and enabled its "sync to android" feature that exposes tuta contacts to the system and other apps.
various other apps like fairemail and google contacts can see my tuta test contacts in realtime (i.e. with additions or changes)
my Simple Contacts Pro does not show Tuta as a source to enable and does not show the contacts in a search, even after an app restart, cache clear, and phone reboot
I just installed the Tuta app from the Play store, made a test contact, and enabled its "sync to android" feature that exposes tuta contacts to the system and other apps.
Discussion about this issue in tuta repo (dev says it's a contacts app issue, not tuta)
Samsung s23+, android 14, belgium (english)