Bug#971444:
Using the recipe from the OP, it works fine for me in Emacs 27.1.
Bug#971444: emacs: cannot set a custom theme using only the menu bar
Package: emacs Version: 1:26.1+1-3.2+deb10u1 Severity: normal Dear Rob, It is not possible to set a custom theme using only the menu bar and without setting it by hand in init file. The theme will be applied but after restarting Emacs, it won't be loaded automatically. This bug only applies to