With emacs -Q evaluate

(set-frame-parameter nil 'menu-bar-lines 27)

This corrupts the display when I start moving point upwards as in the
attached screenshot.

martin

In GNU Emacs 31.0.50 (build 9, x86_64-pc-linux-gnu, GTK+ Version
  3.24.38, cairo version 1.16.0) of 2025-03-14 built on restno
Repository revision: 1437fc2bca2e42cd2a28754bbb4d9ac1403b87b7
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
  'configure --with-gif=ifavailable --with-tiff=ifavailable
  --with-gnutls=no --without-pop 'CFLAGS=-O3 -g3 -no-pie''