USB-C to 4k monitor: right 1/3 not working

[robt]

Again, I am using only an external 4k monitor, not the PBP screen alongside the external one. That should work, but doesn't. If anyone knows whether the standard manjaro works or doesn't work with a single 4k monitor, please report it here (I searched the forum but couldn't find anything). If anyone has success with a standard iso image on sd card that I could easily try, please also report.
Thanks for any and all information - I'm not sure my PBP is the problem (hardware or software) or my adapters...