It bears repeating, many people who think they have burnout actually have chronic fatigue (CFS/ME) but don’t know it yet. Repeated burnouts may simply be a relapse and recovery cycle. A number of the genetic predispositions to CFS also tends to have behavioral components (anxiety disorders and ADHD) that include a preference for a career in software. Now with Covid many of those who may never have had CFS are finding…
CFS does not have a specific treatment. There are standard courses that are recommended, but there is no consensus on how to treat it. Usually treatment involves treating underlying disorders such as depression.
Burnout is a stress response. Unlike CFS, you should improve with rest and taking time. Note that this doesn't mean you are going to go back to a hundred percent because you take a few days, but seeing improvement on vacation is a good indicator of burnout.