I am using an Intel 2 port X550 network adapter with VLANs. Should I enable VLAN hardware filtering or leave it disabled.
x550 supports it. ix driver should support it.
You can try it and see if tagging still works ok.
However, stuff like zenarmor may be an issue. Depends on what you are running (not running), etc.
https://www.zenarmor.com/docs/guides/disabling-hardware-offloading
If OPNsense gui allows you to do the cfg there, great, if not you can do it manually.
https://www.siberoloji.com/how-to-configure-vlan-tagging-on-freebsd/