How is that compatible with the GDPR which has been interpreted by courts in a way that it forbids sending any network packets to the USA, no matter if the user consented to it or not?
For reference, see the rulings which deemed Google analytics illegal independent of consent.
Something along the lines of "we can't identify the device so we have to count it as a unique install"
The post you're replying to seems to be more meaning "they shouldn't be receiving any information from (un)installers anyway".
So, them being able to count installs at all is the problem.
Source: https://forum.unity.com/threads/unity-plan-pricing-and-packa...
use data in compliance with GDPR
But the curts have ruled such claims from US companies are worth nothing because the US government has access to that data and has not made such claims.
Therefore it is very likely they will rule the same for "IP soandso installed software soandso".