I also have a 2020 XT and haven't noticed a strong/very heavy gas smell on startup in my 1300 miles or so of driving it over 6 weeks.
You should contact the dealer to document the issue. In numerous car forums for various brands people notice gas smell on startup. Sometimes it's an actual problem - a leak of some kind, and other times there's no apparent problem aside from the smell itself. Unless you let Subaru take a look at it, there's not much use speculating.
Document each time it happens, so that when you do take it in to the dealer, you have a record of the circumstances, e.g. cold start in the morning.
The dealer will inspect the fuel system, check codes, and if they don't find anything, they'll try to replicate the problem. The more detail you give them, the better chance they will have of discovering the same issue. If the issue is intermittent, like only once a week, then it will be hard for the dealer to replicate, unless there's some condition that's different that time - for example, filled up the tank the day before, or the tank was almost empty, or the temperature was below freezing, or you used a block heater, or the car was parked on an incline that time, or the car hadn't been driven for 36 hours. Any potential set of circumstances that will let the dealer duplicate the problem will help them diagnose it.
Hoping that it doesn't happen to you again, but if it does, you should take it in. It's not a normal startup smell in the Subaru XT, nor is it a known problem that they can easily diagnose, but Subaru is aware that some customers have had this issue in the Subaru Ascent, that has the same engine. I don't believe they've isolated a single cause yet, so again any documentation you provide might help them uncover what is happening in yours.