I am using the TPLink Arche C7 and made it as Wireless bridge using this guide https://openwrt.org/docs/guide-user/network/wifi/relay_configuration and worked fine.
The client connecting to the above router is getting same MAC address of the router with different IPs. for example, my laptop is showing router's mac, same problem for all devices connected to the router. How to fix it?.
As stated in the guide:
If supported by both devices, consider using WDS, Layer 2 GRE tunnels (“gretap”), or mesh networking.
relayd works at Layer 3, so all clients have the same MAC when you check the upstream router's ARP table.
any fixes?. Or that's the way it works?
An AP-STA link assumes that everything on the STA end is one MAC address, as would be the case usually when the STA is a single machine like a laptop. The standard doesn't provide for sending a "final destination" MAC which would be necessary to have a true layer 2 bridge.
If your AP supports OpenWrt you can use other linking standards as mentioned above. If it's a typical ISP provided box with closed firmware you are stuck with either relayd, or moving your whole network to the LAN side of your OpenWrt router and using the ISP box only as a source of Internet.
My AP is TpLink EAP245 with original firmware. Can I use Openwrt in the client router TP-Link Archer C7 with mesh?
You need to have a Openwrt mesh running on the AP too to use the mesh in client router?