It only kicks in after you make a certain revenue with the game (200k USD for Unity Personal and 1Million USD for Unity Pro). So if revenue is 0, it will never kick in.
Until you make 200k you don't get charged. So you're likely fine to release it and if it's successful port it to a different engine before you hit that.
Problem is that if you intent to monetize it then you might "accidentally" make a good game that is installed a lot and maybe you charged 5$ upfront via steam. Now you come by the 200k$ threshold and have to pay steam 30% and assuming worst case you have 500k installs.
Meaning you owe now unity 100k$.
So 200k - 60(steam)-100k is 40k$
You have now 40$ left to produce your game.
Even worse. If you have now stopped selling the game due to reasons. People reinstalling it will cost you 20 Cent
When I opened GitHub this morning, Godot was the #1 trending repository. So yeah.
Everyone with half a brain could have seen something like this happen from a mile away but yet here we are. If you lock yourself in with a proprietary vendor, they can screw you over later. See also Reddit. And if I were to venture a guess the same will happen with Discord.
I was also going to use unity for my video game, but as I saw that unity changed their policy, or is going to change it too the worse in January. I’m going to stick with Godot.