Ah ok, thanks I will try that firmware selector. The WA-901ND page does state that
Starting with version 19.07.4 OpenWrt supports these routers with the new target ath79-tiny, but standard images will be too large. However, you can build own images using the respective ImageBuilder. For instance, to build an image for WA901nd-V5 including LuCI and excluding PPP use the following command, see detailed instructions under build your own image:
make image PROFILE=tplink_tl-wa901nd-v5 PACKAGES="uhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap -ppp -ppp-mod-pppoe"
There's even a link to a still active thread !!
I'm going to give that a try