My password is not accepted because it is too long
In password security, the longer the better. With a password manager, using more than 24 characters is simple. Unless, of course, the secure password is not accepted due to its length. (In this case, through STOVE.)
Possibly indicating cleartext storage of a limited field (which is an absolute no-go), or suboptimal or lacking security practices.
Your password MUST contain big and small letters, and contain at least 1 number character and 1 spacial character, it MUST be 8 characters long, and it MUST be typed on a German Cherry keyboard between 8-9 PM, using ONLY 1 finger while blindfolded and listening to ABBA music. BUT NO SPACES ALLOWED!!!
This is because of something called entropy we never even read about so we have zero understanding of it. Of course combined with lousy programming, so safety is all on you.
Making all these possibilities OPTIONAL would actually make for safer passwords (higher entropy), as would using multiple words separated by spaces. The only meaningful way to accept a password would be to test it against common bad passwords, and test the entropy to determine acceptable levels. There is no good reason a password couldn't be 10 words and at least 127 characters. There is no way that should stress a properly designed modern system.
the guidelines that NIST, Microsoft, GCHQ and a few other institutions now recommend for password security
Because they are morons that don't understand entropy.
Requiring at least 1 number increases entropy less than simply allowing the use of numbers, and then recommending it.
But most password queries are lousy at describing what's allowed when creating it, and they generally don't describe it at all when you enter it for access.
The second part can be crucial for remembering exactly how the password was created, because what is now required, used to often not even be possible to use!