Check if WR744WSGV-V3 is in OpenWrt target/linux/ramips or ath79 . If not, create a new device .dts file and add to target/linux/ramips/image/mt76x8.mk .
If the manufacturer has not released a update in over two years, it is time to consider replacing the hardware. Modern threats evolve faster than legacy firmware can be patched. wr744wsgv-v3 firmware
Request GPL source from the manufacturer (required by GPL for Linux kernel). Often provided as a tarball with kernel + driver patches. Check if WR744WSGV-V3 is in OpenWrt target/linux/ramips or