Samsung TV "Mode not supported" error

This just started happening today, and is apparently a common problem with no specific solution.

My Samsung TV, quite a few years old now, is suddenly showing this error when I try to use previously working devices via HDMI. This is happening with several devices across several ports. I first noticed it when trying to connect my Switch, which I don't do that often, and neither my PS4 (same HDMI cable) or Virgin TV box (different cable) work, everything shows this message with a suggestion to change the output resolution. Any ideas? The TV menu is very limited and doesn't allow resolution change afaik. Thanks!