>>> (65).to_bytes()
b'A'

It seems like your proposal is mostly guided by: convert an int to a byte (bytes string of length 1). IMO this case is special enough to justify the usage of a different function.

What if people expect int.to_bytes() always return a single byte, but then get two bytes by mistake?

ch = 256
byte = ch.to_bytes()
assert len(byte) == 2  # oops

A function dedicated to create a single byte is expected to raise a ValueError for values outside the range [0; 255]. Like:

>>> struct.pack('B', 255)
b'\xff'
>>> struct.pack('B', 256)
struct.error: ubyte format requires 0 <= number <= 255