Only the beta version of FTLDNS works with custom DNS ports.
The version you are on doesn’t.
If you want to try the beta version of FTLDNS, use these instructions:
https://discourse.pi-hole.net/t/help-us-beta-test-ftldns/
Also use this guid to properly pair unbound and Pi-hole FTLDNS:
https://docs.pi-hole.net/guides/unbound/