can't delete part name on staffs

On a score or parts, the part names will not delete on the first staff, nor the abreviated part names on subsequent staves. Normally, I highlight the name and press delete. that no longer works. I just installed the latest build: OS: Windows 10 Version 2009 or later, Arch.: x86_64, MuseScore Studio version (64-bit): 4.3.0-241231433, revision: 5f36e74

I am using Windows 10. The attached file has this problem, but I have tried this on other scores and experienced the same problem.

Thank you for your attention.