From today I have the same problem with mine RX 580 4GB Nitro connecting with tv via hdmi. Yesterday it worked. Tried 20.4.2 and 20.4.1, same issue. Uninstalled amd software. Very frustraiting
The only work around I have is to use a a DVI to HDMi adaptor and take the signal from DVI to the TV.
This is super lame as it restricts me to a max resolution of 1080p, but at least I have an signal.
Interestingly the DVI to HDMI setup results in a "No Signal" condition for POST. Once POST is complete and the windows boot starts the signal is found.
Not impressed with the lack of official response on this.