It's thermal throttling, i.e reducing compressor speed to prevent over-heating, because it's not designed for such extreme temperatures. User manual clearly mentions that it's optimum performance is upto 43C outside temperature.
The issue has been clearly discussed previously.
I used to live in single story house, hot like oven and direct sunlight throughout the day, with temperatures going 45-50C on regular basis, and regular non T3 split AC would lose cooling and even start thermal tripping occasionally (inverters were not available back then).
Nothing can be done, except cleaning outdoor unit coils every month and keeping some shade on outdoor unit. This will improve.
Spraying some water carefully on outdoor unit coils will bring some temporary improvement, but i don't recommend it doing with AC on.
Summary: Poor underperformer overpriced "GREE" could not tolerate such high temperatures".