How do I create a data validation list WITHOUT using cells?

Unless you mean something else, no need to wrap in quotes, or use the "=" sign

You can put them in as a comma separated list:

true,false
yes,no
2,4,6,8
with space,without

etc.

So for anyone who might have run into this problem, I found the solution (or rather the cause).

I had previously tinkered with the locale parameters of my system and altered the list separator character to semicolon in Control Panel > Clock & Region > Region > Additional Settings. When I used that instead of comma, the dropdown worked. The question is now whether this will continue to work on a system with the standard separator.