You can link your PSN and Steam accounts with GoG Galaxy 2.0. Ive done it. I presume you could with Xbox and other launchers as well.
As you can see above, I have PS exclusives and PC games that aren't on PSN here. You install Galaxy 2.0. Go to settings, click "Add Games and Friends" then click "Connect Platforms." Once there you will see a list of the platforms that can be connected with GoG. It includes all the platforms CP 2077 is being sold on. Each platform you try to connect will of course require your user name and password. You'll be able to launch PC games from within 2.O (assuming they're installed on your PC). If they're not installed on you PC (i.e. for me - my PSN games), they're mostly just there for the decorative purposes of seeing all your games in one place. However, I presume that by linking your accounts up in this way, you get the Cyberpunk 2077 goodies for linking to your GOG account.