Parity and stop-bit options that were available in 4.9.x were added to
the screen-v4 branch after screen-v5 diverged:
https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=8b386d8
"Support stop/parity bits on serial port"

Specifically, these were lost:
- cstopb / -cstopb
- parenb / -parenb
- parodd / -parodd

Serial setups that need e.g. 7E1/8E1 (or explicit stop-bit control)
cannot
be configured via screen options anymore.