I guess it will be a bit annoying that there will be slightly less LGBT people tens of millions of years from now compared to today. I will set an alert if you want.
You are talking about an insanely small effect that requires a precise sequence of events
Company makes a pernatal LGBT test
The product actually works, which holy shit no it won't. It is way more complicated than screening for say Down syndrome.
It is widely accepted as working
The average human on earth makes a few dollars a day and yet they have the money to pay for this and do reproductive counseling and decide to abort on this
Somehow someway all 8 billion people have this removed from them and it is maintained for tens of millions of years to get enough distance between those future humans and us to prevent random mutations from reverting it. Hell chickens are still born with teeth in rare occasions. That is a 80 million year reversion.
So yeah not worried. If you need something to worry about you can read up on climate change.