I honestly don't know much about it, but from what I've heard, there's many factors that can affect your HRV, including things like anxiety, time of the day, excitement, caffeine, poor night of sleep, hard training, etc. Apparently some people want to use it as a way to assess the stress of a training program. So, in theory, a poor score would indicate you need a deload or something similar. It seems like this is disputed since the devices vary in their accuracy. It also seems like it's hard to know what caused the HRV variation and some say the correlation between fatigue and HRV is poor in the first place, since HRV can be affected by many things.
Additionally, there's also the possibility of mindfucking yourself into performing poorly, just because the device told you that was supposed to happen. This is a cool article on that effect:
https://www.barbellmedicine.com/blog/placebo-sleep/
As a complete broscientist it seems to me that, if you're getting some annual medical check-ups with a blood panel, blood pressure and other common sense stuff to make sure you're generally healthy; and have a generally healthy lifestyle, micromanaging these "fatigue indicators" day-to-day might end up doing more harm than good, and you might be better off measuring fatigue in other ways and not wearing these devices at all.
Maybe if you were a coach gathering information from a high level trainee, or if you were a researcher it would be interesting, but as a way of self monitoring it seems to have limited usefulness.
Hope you don't die.