Yeah, I do/did doubt this would port over the Alt Codes, though as you say I'm not sure someone couldn't just long-hand re-write the Alt Codes in either a mod/add-on/config file for any given Office competitor suite.
After all, the majority of the "mappings" are arbitrary/obscure anyway as only one option can "match" the letter (e.g. F is for File, so ForMulas needs to use M. I and D are used for legacy Office Shortcut compatibility so iNsert and dAtA use N and A respectively).
In other words, looking for a logic to these codes even in Office is a hiding to nothing anyway and it's really just a case of building muscle memory (or coming up with a bizarro-logic that helps e.g. "A is for dAtA").
It would be incredible to just be able to install a "365 Mode" or config where the full re-map has been done. I'm semi surprised this hasn't already existed for a long time, even to the point of being shipped built-in.
Interesting they kept that, I really feel we lost something when we lost menus that underlined the shortcut letters you use for them.
I wonder how they implemented "alt codes" is some remnant of the menus still in there (if only from some accessibility feature".