Proxmox + OPNSense and FritzBox

[Calautigo]

Hello,
I'm a little bit desperate. I have an OPNSense Firewall, a FritzBox 7530 and my home network behind the firewall. The FritzBox 7530 is setup in bridge mode on port 2 (I cannot verify this, my ISP said it is on Port 2 in Bridge Mode, but I can't find this setting)
My ISP said, that I don't need any login data, I connect my OPNSense WAN port on port 2 of the FritzBox and all should be fine. I set my WAN Port on OPNSense on DHCP and I get my static ip, which is the right.
I can ping and curl Google sites (also Youtube), and most sites which have http connection. Sites with https timed out. Also the other ones are very slow to load (www.derstandard.at works, but slow; news.orf.at don't work)
Yesterday I got this new FritzBox modem, before that it was a technicolor modem which I set in single user mode and OPNSense has made a pppoe connection. That worked flawless.

My OPNSense is a VM on a Proxmox Server. The WAN network is a bridge with only the port set in the bridge. I connected my laptop directly to the FritzBox same behavior.

I don't know what to do anymore... This is very odd... Oh the hardware offload settings are disabled (the checkbox is checked in opnsense). I also done the netsh winsock reset, ip reset and flushdns.

We have quarantine here in Austria and without internet its very boring.
Thank you for your help!

[Calautigo]

Ok, I let my ISP turn off the bridge mode and use the Exposed Host Setting. But here is the next problem: My internet speed is very very slow behind the opnsense firewall. When I connect my laptop to the FritzBox directly, then my speed is at 80Mbit, behind the firewall only 5Mbit.
I don't have intrusion detection on or such a thing.