Model DIR-853/ET Hardware Version: A4

I need openwrt for DIR-853/ET Hardware Version: A4

What does https://openwrt.org/toh/start say?

The A4 is not supported by OpenWrt -- if it was, it'd be listed in the TOH:

There is a thread where it appears that people had some success modifying the A3 image... check that out here (use this method at your own risk):