Using OpenWrt to extend Fritz!Box wlan

I have a TP Link TL-WDR4300 (two radios) with OpenWRT 22.03.3 I used as router for my fiber connection.

After a fiber upgrade the company now supplies a Fritz!Box 7590 as main router which performs OK.
However, I have a weak (2.4 Ghz) signal on the attic (and no option to draw cables). I have 5Ghz connection on the first floor.

How can I configure OpenWRT on the TP Link as bridge connecting to the Fritz!Box using wireless 5Ghz and forward the connection using the 2.4 Ghz radio of the TP Link. Is this possible at all?
I don't need a performant solution. just a stable signal.

if all devices should be on the same LAN -

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Ne aware that relayd is kind of a kludge, yes it works, but it isn't without problems (IPv6, multi-cast, ARP, etc.) - WDS/4addr (not possible with the Fritz!Box 7590 and its vendor firmware; you'd have to replace this one with an OpenWrt capable device of sufficient performance) or routed client approaches would be more stable.

I would do the opposite.
keep the TP LInk as your router for fiber connection.

set the fritzbox as an IP device. it will receive an IP from the openwrt router and you can either connect to lan1 interface or via wlan

i actually run this configuration but I do via Lan by connection an ethernet cable to lan1 of the fritz!box router.