Are the keyboard and screen from a2019 compatible?

Yes and no. the display will work for some functions but not others. Things like True tone, camera or ambient light sensor will generally not work properly due to different parts in the display assembly. I haveheard that it can cause some issues in general, so even if the display works, I would not really say they are compatible. Okay for testing, but not to install in a machine as a permanent fix.

Keyboard meaning the keyboard? Or keyboard meaning the top case. The keyboard itself? Probably? The whole top case I would be hesitant to say is compatible. Also there are 2 variants of 2019. There's a 2 Thunderbolt port version, and a 4 thunderbolt port version. Both have a touch bar. The 2 TBP version topcase would definitely not be compatible, layout is totally different on the internals. But the 4TBP version you might get away with? I haven't found any definitive information saying it's not.