Firmware Tcl 20 5g Link -

You can download the Mobile Upgrade tool from the TCL website and install it on your PC. This tool allows you to flash the latest software by following step-by-step instructions via a USB connection. Firmware Resources

Source: Based on standard TCL 20 5G (T781) user manuals and software specifications.

Use simg2img + mount to explore build.prop, init scripts.