pressing twice is twice the wear on the FOB
I haven't looked in my 2018 fob but I'd expect it's simple to solder a new switch under the button, just like you would do with eg a worn-out switch on a computer mouse.
If you don't want to do that, you go onto Amazon or wherever and order a new fob from Denso or whoever makes it, the model number is already on your fob, and you snap off the Subaru logo from your current fob and snap it onto the new one, and get your car to learn the new fob. Done. Note that I've never actually had to order replacement fobs, but this is the route I'd go, and I'd expect it to work.
More important than the fob though, is that the double unlocking wears out the solenoids in the car. In my 2007 I chose to unlock/unlock the driver's door only with the first press. I believe choosing between the driver only, or all doors, for the first press, was configurable, but I don't remember how, or maybe it was configurable by the dealer. The car did not have pushbutton start or keyless entry. In my 2018 I choose to lock/unlock the driver's door only with the first press.
The wear and tear is as follows: If you need to lock/unlock the driver's door twice to actuate all the other doors, there is double the wear on the solenoid in the driver's door. Mine eventually failed in my 2007 and I had to order it, and the dealership got me the wrong part, so I was using a mechanical key to lock/unlock and arm/disarm for a week and a half while I waited for parts. And I was driving around with my door all apart. I think the solenoid was about $70 CAD and an hour or two to open up the door and replace it. However, if you are usually the only one using the car, actuating all of the solenoids in the car puts extra wear on all of the other solenoids.
If you need to replace the switch in the fob, it's a couple bucks and a few minutes to replace it. It's a lot less work than replacing the solenoid in the door, and replacing the solenoid is not a big deal either.
And it's not exactly "twice" the wear. You may need to unlock twice, but when you lock, it's a single press that locks everything, and if you are the only one in the car, actuating all of the solenoids causes some wear to all of them even if only the driver's door needs to be locked.
And if you use the sensor on the door handle (if equipped) to lock/unlock, you don't wear out the fob at all.