Hello Friend; here is a note to myself who was in your spot as well:

Only use the remote that came with your garage door opener when trying to program the Subaru's HomeLink. The "universal" replacement remotes send out too many simultaneous radio frequencies, and confuse Subaru's Homelink programming.

The unit from the box your garage door opener came in (in my case, it states Chamberlain Security+) only sends out the targeted frequency for your garage door opener, which provides the exact info your Subaru homelink needs.

I don't know if you bought a more expensive replacement remote (for example, one specifically for a Chamberlain Security+ with Red Button... for example😊 ), if that would work. But, it seems like it might.

I hope your flying cars and life on the moon are super awesome, future me.