Did the upgrade to 26.1.3, everything so far was working, except a home grown automation to sync stuff gathered from the OPNSense API, Portainer, and kept in a Redis Cache to my BIND setup. This is done by a Python script.
In a most strangest interaction, use case testing Python using requests, http, or httpx and was not able to reach and more correctly connect to OPNSense's API, but Postman/CURL both could - and got valid responses back. Tested the HTTP/1.1 or HTTP/2 nature, always worked for Postman and CURL, never worked for Python.
So I went back to the OPNSense, maybe I could re-reset some stuff, started simple - restarted the System Configuration Daemon and then Web GUI services from the Web GUI, suddenly Python is working again.
Also did a another restart of the OPNSense (it restart initially after the upgrade), and the issue did not present itself again. So this is just a heads up to any that might hit whatever edge case I did, restart services and/or host, should work again.