@Gabi_me 

Archer AX80 is not in the EasyMesh compatibility list: TP-Link EasyMesh Devices.

For OneMesh, nornally OneMesh could only connect one router and extenders, instead of two routers. However, some users have found a workaround to add EasyMesh router to OneMesh router successfully via WPS, you could refer to this post for a try.

That is to say, use your Archer AX80 as main router and use AX55 as satellite router.