Not that they can really know, but most I've seen is that they disable pasting anything into the website, effectively making banking super slow for us with password managers and long passwords.
Fortunately, my bank doesn't disable pasting (Banc Sabadell in Spain). Instead the password is restricted to maximum 6 numbers for login. Yay banks!
In Firefox, at least, there is an about:config option to turn off the ability of webpages to disable paste. Flip that setting and managers work again on those pages.
6 characters? Let me guess, were there restrictions on character space and case?
One place I had an account has a password input that restricts all of those, so it's like an 8-10 character string of all capital letters. I don't understand it at all.
Fortunately, my bank doesn't disable pasting (Banc Sabadell in Spain). Instead the password is restricted to maximum 6 numbers for login. Yay banks!