OpenGD77

this radio uses the Auctus A6 chip, it is used in a variety of low cost DMR HT besides Baofeng.

A ham in the United States dove pretty deep in another radio using the A6.

Here is a good collection of info on the A6

https://jhart99.com/auctus-a6/
https://jhart99.com/auctus-a6-revealed/
https://jhart99.com/a6-hidden-interface/

https://jhart99.com/radiodump/

https://jhart99.com/burn-rom/

Some info on that radio with the Auctus chip, which may be of interest to GD77 users: the battery looks as it could be compatible, it actually fits in and can power the GD77, but does not lock. The contact plate is a tiny bit too thick for the battery to fit in the GD77 all the way.

Other info, which is probably only interesting to buyers of that radio:
1: I looked at harmonics with a Tiny SA ultra. Transmit seems quite clean. Note that Baofeng quality control has bad reputation so other radios may be different. And the Tiny SA can only measure so much, so take that measurement as an indication that harmonics are not catastrophic, that is all.
2: the data cable from the Radioddity GD-88 works to program the radio. That cable has a USB to serial converter and, apparently, connects the TX and RX line as needed by this radio.