Yep, they put in a lot of effort into the security and open source stuff, but at least on Graphene, the bundled apps are severely outdated aosp apps, they don’t even support material you, meanwhile current aosp apps do support it, as can be seen on Lineage. The calculator app looks straight from Android 5 or probably earlier.

I’m not sure but afaik CalyxOS and LMODroid does that.

Most of the time I find this stuff on 4pda. Sure it’s in Russian and it requires an account to download files, but they delve much deeper into the device and usually you’ll find working instructions how to unbrick stuff.