pfSense

After #9548 the test which restricted it before is no longer present. The change suggested on that blog post is no longer necessary on 2.5.0 as there is no testing made except to exclude virtual interfaces like IPsec VTI

Xen was excluded from VLANs years ago because the driver had stability problems with VLANs (See #4103 for example)

Making the change suggested by that blog post on 2.4.5-p1 should work:

diff --git a/src/etc/inc/interfaces.inc b/src/etc/inc/interfaces.inc
index df8abd937b..84304f78a8 100644
--- a/src/etc/inc/interfaces.inc
+++ b/src/etc/inc/interfaces.inc
@@ -6795,6 +6795,10 @@ function is_jumbo_capable($iface) {
         return true;
     }

+    if (substr($iface, 0, 2) == "xn") {
+        return true;
+    }
+
     return false;
 }

As there is nothing actionable here, I'm closing it out. If the above change doesn't work, make a post on the forum asking for assistance.