when regular dns and doh dns are both set, the first responder is DoH DNS, How to change it priority?

You can't change that. If DoH is configured, regular DNS settings are ignored.

Which is fine that way.
Really annoying is the fact that FWD entries for specific forwarding are ineffective as soon as DoH is enabled. Any chance to change that?

You can't change that. If DoH is configured, regular DNS settings are ignored.

In other words, doh cannot be used as a backup dns server(second dns server)?

No.