So with all the new rules after C19 has anyone flown (IF you could get on the plane) with the FOX transition bag rather than just a small helmet bag?

This one

https://www.leisurelakesbikes.com/317064/products/fox-transition-duffle-bag-black.aspx

had no issues with this when you could put it in the overhaed locker

IF they check, they won’t allow it. You can look up the permissible size but IIRC the depth of the bag must be <20cm.

IME of a couple of flights recently, no one is checking where you put your bags once you’re on the plane, but on a busy flight, staff were eyeballing everyone’s bags at the gate and testing the ones that looked dubious.

Option B is to wear the helmet and squash the bag down, at least until you get past the desks.