I just got a Hakka MX for a gravel bike. It has through axels and in particular the front wheel has a 12mm x 110mm axel. I carry my bikes in the bed of my pickup with a canopy and use a for mount and wheel hitch holder for the front wheel so that I don't have to lay the bikes down. The wheel carrier is designed for my road bike which has a skewer. I did get an adapter for the fork mount so the bike is stable. I have looked but can't seem to find an adapter so that I can safely carry the front wheel.

I'm looking for solutions. I don't want to chance damaging a spoke by having the wheel bounce around on rough roads.

You can get a quick release adapter that slides into your wheel axle - we've used that with our Thule wheel carriers (the flexible arm ones). There is also a rigid thru axle wall mount that I've seen, so I just searched amazon for wall mount wheel holder and came up with a Lindarets Narwheel Wall-Mount. That looks like something you could mount in a pickup bed.

I use these giant wire tie things. You can get them at any hardware store. I secure the wheels to my fork. You could do the same to your frame or any other anchor point.