Signing algorithm not accepted
What it means
The server does not list your alg in token_endpoint_auth_signing_alg_values_supported, or the alg does not match the key.
Fix
Use RS384 (RSA) or ES384 (EC P-384), whichever the server advertises.
Check it with smart-doctor
Run your login and smart-doctor ranks this cause against the others, with the evidence it found.
npx smart-doctor check my-profile