hey, i got a tplink tl-wa850re repeater and connected it to my openwrt router.
but if i try to ping a client behind the repeater i get the following:
64 bytes from 192.168.1.243: seq=138 ttl=64 time=8.788 ms
64 bytes from 192.168.1.243: seq=139 ttl=64 time=9.346 ms
64 bytes from 192.168.1.243: seq=140 ttl=64 time=9.111 ms
64 bytes from 192.168.1.243: seq=141 ttl=64 time=9.448 ms
64 bytes from 192.168.1.243: seq=142 ttl=64 time=9.216 ms
64 bytes from 192.168.1.243: seq=142 ttl=64 time=11.206 ms (DUP!)
64 bytes from 192.168.1.243: seq=143 ttl=64 time=9.837 ms
WDS was apparently intended to resolve this kind of problem. However, the spec doesn't say how to use the addressing the spec provides, so each vendor's implementation is different and some don't interoperate.
If you want on-link services, such as mDNS or Windows browsing, you need a layer 2 ("raw frame") bridge. You also need a layer 2 bridge if you want smoother roaming, so that the clients don't need to acquire a different DHCP lease when transitioning from AP to AP. Layer 2 bridges that might work for you include:
WDS
batman-adv
GRE tunnel
Layer 2 VPNs, such as OpenVPN "tap" (Wireguard is layer 3 (IP routed) only)
I think it unlikely that the TP-Link firmware is able to supply any of these. A quick search on "tl-wa850re WDS" didn't instill a lot of confidence (though you may wish to look into things more deeply there). OpenWrt firmware for the TL-WA850RE may be an option, but given that it is a 4/32 device already on the "tiny" target, extensibility and stability are likely going to be very limited.