Most modern GPUs are set to turn their fans off at temps at/below 55C.
They adjust fan RPM to maintain around....74C
Anything under 80C is perfectly acceptable.
If you see 85C or higher that generally means the GPU fans are spinning at full speed and still not able to keep temps in check. This is usually attributed to poor case airflow, but can also be a result of a sub-par thermal solution on the GPU. Applying new thermal paste on the GPU (in my experience) can lower GPU temps (or fan speed) drastically. My last card (MSI RX480 GamingX) was running 85C at max fans (2400rpm or so) after a year of usage. I repasted, and temps immediately dropped to 73C at 1100rpm.