In your initialization file, bind the Transient casual-html-tmenu to your key binding of preference.
(keymap-set html-mode-map "M-m" #'casual-html-tmenu)
A different binding (M-m) is used as casual-html-tmenu is intended to work alongside with Casual EditKit.
It is convenient to also bind casual-html-tag-tmenu as well.
(keymap-set html-mode-map "C-c m" #'casual-html-tags-tmenu)
If HTML Tree-sitter support is enabled, use the keymap html-ts-mode-map in place of html-mode-map.