Brand exclusions in PMax look like the clean fix for a store with strong brand demand, but they're messier than they seem. Excluding brand terms can still leak brand queries through shopping and display placements, and you lose sight of how much revenue was brand demand to begin with. Leaving brand in has its own problem: PMax takes credit for sales you'd probably get anyway, so ROAS looks better than the incremental value really is.
My leaning is to keep brand traffic in for a quarter, pull the brand vs non-brand split from the search query data, and only exclude once you know what share of conversions would have happened without the ad. How are others handling this when brand search volume is high?