I'd sent a help message to the forum and Christoph Siedlerchr responded with a confirmation that it is still not working in the latest development version, and a request to post a bug report.

Some keyboard shortcuts are NOT Working:
e.g. (these are the only ones I checked, not sure about others)
Keyboard binding: Cntrl+shift+A Action: Create new article
Keyboard binding: Cntrl+shift+B Action: Create new book
Keyboard binding: Cntrl+shift+I Action: Create new inbook
Keyboard binding: Cntrl+shift+M Action: Create new masterthesis
Keyboard binding: Cntrl+shift+T Action: Create new phdthesis
Keyboard binding: Cntrl+shift+P Action: Create new proceedings
Keyboard binding: Cntrl+shift+R Action: Create new report
Keyboard binding: Cntrl+shift+U Action: Create new unpublished

but
other keyboard shortcuts ARE Working:
Keyboard binding: Cntrl+N Action: Create new entry (brings up the menu to select type of entry)
Keyboard binding: Cntrl+shift+N Action: Create new entry from plain text
Keyboard binding: Cntrl+E Action: open editor of highlighted reference

JabRef version
JabRef 5.0–2020-03-06–2e6f433
Windows 10 10.0 amd64
Java 13.0.2