vLANs not working (untagged switch)

Hello

I had a working vLAN for some Test-VMs (eg Firewall OPNsense) working on Proxmox 6.x.
With 7.x I have NOT been able to get my vLANs working again.
The vLAN does work if I configure it on my Macbook or another Linux / Windows box.

But NOT on the Proxmox.

I would like to use 2 vLANs:

A vLAN99, untagged on the switch, connected to the LAN vmbr0 of all three Proxmox - this serves as a "Internet" connection to test firewalls/vpns.
A vLAN98, untagged on the switch, connected to the LAN...

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