Which DNS is going to be used if I have different DNSs set in KDE's Network Manager for Wi-Fi and VPN connection?

systemd-resolved only supports plain DNS and DoT, not DoH.
The leading dash means that DoT is disabled on that link.

If you actually need DoH, enable it in the browser settings.
Or configure it globally with a service like dnscrypt-proxy.

See also:
How do I use a DNS-over-HTTPS as the default DNS server system-wide (not on per-connection basis)? - #5 by vgaetera