

One character equals one byte of memory so my guess is they only allocated 16 bytes of space for the password.
This is true for storing text in general but passwords aren’t supposed to be stored as text, they should be hashed. The size of the hash will depend on the hashing algorithm. In other words, if there’s a database limitation for the size of a password, it probably means they’re storing the password plaintext 💀
More likely than not it’s just some poorly designed validation
Most places aren’t hiring right now because of economic uncertainty, even with job postings listed. If you were getting interviews from your resume before, you probably aren’t doing anything particularly wrong.
Also, 100 applications in a year isn’t a lot. You’ll need to crank those numbers if you’re in a rush to find something.