gk7ncklxlts99w1 Are directories such as Music, Podcasts, Movies intended for app data or for users? Is it safe to use those directories myself?
Yes, its safe.
What is Settings > Passwords & Accounts? I really have no clue what this is. Under Passwords, passkeys, and data services, selecting an app such as Firefox brings up a prompt which says "New passwords, passkeys, and other info will be saved here from now on. Firefox may use what's on your screen to determine what can be autofilled". Is this primarily for form autofill?
Yes, I believe its the autofill framework. As for Passwords and Accounts in general, its an area for the storing of credentials that can be used across apps, e.g. a Google account for usage across the Google app suite.
Option to export SMS and call history. We can already export contacts to .vcf in the Contacts app, so it's odd that we can't also export SMS and call history. The reason I deem this important is because I don't want to have to rely on the SeedVault backups, because SMS messages never finish backing up so I'd consider it unreliable or maybe even corrupted. Contacts and call history appear to backup fine but manual export should still be an option.
Obviously doesn't solve the issue of support for exports in the default apps, but you should be able to use third-party apps such as Fossify Phone/Messages which have export and import functionality. Once export/import has been done, you can then return to using the default apps.