I've noticed a similar trend in myself. WFH was, averaged out by day, (to the extent I can objectively do that through my own memory) more productive when I was 100% WFH than now, where I am 40-60% WFH. Overall I think it's probably a wash: I think I'm a bit more focused when in the office now than pre-covid, which makes up for the the less focused time at at home.
However there may be less tangible benefits, even if overall productivity is a wash, to having the WFH times. 1) Is the obvious work/life balance. Everything that comes with the convenience of not having to commute, freedom to intersperse everyday household chores during the workday even when it means extending working hours a little later, etc. 2) Is that when I'm WFH I seem to be a little less concerned with the immediate work issues and more likely to drift off into peripheral & speculative projects, things that may yield less results in the short term but might (too soon to really say) yield more in the long term.
Overall I think my general output is about the same, but I'm more content, and perhaps (though not definitively) doing things that will be more productive in the long term.
But there are countless different jobs and responsibilities and personalities that intersect in a way that doesn't lend itself to a single one size fits all rule. But unfortunately, "One rule for all" tends to be the top down approach in most work environments.