I'm a little bit confused about these applications' security model. Normally I'd want whatever secrets are kept by these apps never to leak in the iCloud backup

I'm a little bit confused about these applications' security model. Normally I'd want whatever secrets are kept by these apps never to leak in the iCloud backups (secure enclave storage? I don't know). Do they do this or do they do something else? I see that some apps boast about iCloud integration. That is certainly something I don't want. But for the others that don't have iCloud integration, isn't the secure data backed in iCloud as part of the (daily?) device backup? Also, if they don't have iCloud integration, how do you switch devices? Thanks!