I too have this same issue - and have spent much time trying to get an explanation as to how this works. Not sure why there is business use of home category at all. Additionally, a disclaimer or explanation up front that QB SE does not calculate business use of home expenses would have saved an incredible amount of time and frustration.

for those looking for an easy to use spread sheet that calculates the business use of home amount check out Avalon Accounting - https://www.avalonaccounting.ca/blog/small-business-bookkeeping-guide#which-bookkeeping-system

This a free easy to use excel spread sheet.    Interesting they can develop a spread sheet that does it but QB is saying they can't. Curious?????