So without defending Lotus Notes in any way, there was a meaning to the symbols: they were defined by some oneway function from what you were typing. So you would get used to the little symbol dance, and know if and when you’d mistyped

Wouldn't it also allow any onlookers, if they are able to memorize the symbol dance, to derive your password one character at a time by trial and error?

No because it also depended on your computer . I remember when you switched computers it would change

I seem to recall the password was client-side too. So if you had Lotus Notes in a VM and you restored from a save point you needed to remember what your password was when you did the save.