Using Microsoft SIDH library for messages signing SIDH library looks good but lacks documentation and samples.
The only signature-related code was found at http://github.com/yhyoo93/isogenysignature/blob/master/tests/kex_tests.c appeared not able to sign/verify message (just measure abstract performance of some partial calculations).

Thus it's not clear how to mix arbitrary message to SIDH signature and then verify the signaure corresponds to initial message?
SIDH is a key exchange algorithm, not a digital signature algorithm. The way SIDH works is each side generates a private, random value along with a corresponding public value. The public values are exchanged, and from this, a shared secret can be mutually calculated. No signing is involved.

If you need a post-quantum signature algorithm, you would want to look at something like SPHINCS. You can also use a classical, non-PQ signing algorithm if your threat model allows it.