Just posting here to let others know how I solved very similar problem. I had Openwrt firmware version 18.xx initially. Don't recall the exact version. I was trying to upgrade to 21.02.1. At first I tried to upgrade via LuCI web interface. There I have got an error: The uploaded image file does not contain a supported format
Then I tried to upload new firmware to /tmp folder and do: /tmp/firmware.bin
Then I tried to upgrade via LuCI web interface to openwrt-19.07.0-ath79-generic-tplink_tl-wr1043nd-v4-squashfs-sysupgrade.bin and that worked as expected.
When on 19.07.0 I tried to upgrade to currently newest openwrt-21.02.1-ath79-generic-tplink_tl-wr1043nd-v4-squashfs-sysupgrade.bin and voila!
Update (after such a long time): Just downloaded openwrt-22.03.2-ath79-generic-tplink_tl-wr1043nd-v4-squashfs-sysupgrade.bin and did a successful upgrade via the web-interface.
Great.