I looked into this when I went to the bigger tires on my '19 Outback and here is the easiest solution... don't worry about it.
Going from 225/60/17 to 245/65/17 if you're speedo reads 35 mph, you're actually going 37.42. So only about 2½ mph difference.
Reading 45 mph - actually 48.11. A hair over 3 mph difference.
Reading 55 mph - actually 58.8. About 4 mph difference.
Reading 65 mph - actually 69.49. About 4½ mph difference.
Reading 75 mph - actually 80.18. About 5 mph difference.
As long as you are aware of it, you just adapt your driving habits.
Here is a calculator to help. It would just take way more effort to have it adjusted to justify the change. Subaru will be happy to tell you the EyeSight system won't work right, blah, blah, blah but they won't go into the computer to recalibrate the speedometer. For the record, my EyeSight system still works fine. I went from the stock 225/60/18 on my '19 OB Touring to 245/65/17 and my speedometer on the top end reads 75 mph then I'm actually only going 77.38 - a difference of less than 2½ mph. I guess the drop in wheel size made the difference less dramatic. The biggest hurdle I had when I changed wheels and tires was getting the TPMS system to work again. I took my car to the dealer and three different tire shops and nobody could get the TPMS light to go off or could give me an answer of what I could do to fix it. I finally found a solution for it after hours of internet sleuthing and it wasn't what I expected. I had to get the tire shop to program the sensors in the tires for a 2017 Impreza... that fixed it. It's unexpected and strange, but it worked. The onboard tire pressure readout is correct now to what the actual pressure in the tires is as well.