For me, it works excellently with the RT-AX92U, as an ASUS AI mesh AP. Simply start the new AP directly next to the large router. Then the old router recognises the new router via wireless and you can then integrate it configured as an AP. Then move the AP to its new location, connect both devices via Ethernet and you're done.

I use 2 Asus Ai Mesh AX-WLAN systems ZenWiFi XD4 (double pack was in the discount for 160€), but if you have a little more budget, the ZenWiFi XT8 with Tri-Band would be worthwhile (double pack for approx. 400€). In general, you can use all Asus devices/routers for your mesh (also with 1-click installation). Our old AVM Fritz repeaters don't work so well with the router.