Mesh System OpenWrt

Hello, can you please tell me if I have two routers with openwrt firmware, can I combine them into a mesh system? Just so that they are connected not via wifi but via RJ-45 LAN-WAN

Your question is confusing. Mesh is when the routers are connected by wifi. You probably want "fast roaming" setup based on your last sentence.

Maybe you should describe what you're looking to accomplish in layman terms.

ASUSWRT has the ability to connect both routers via RJ-45.

You mean asuswrt have the unique ability to connect two routers ?

They shouldn't be connected lan-wan, but lan-lan, at least when you use Openwrt.

You probably need/want, with 802.11r enabled.