Topic.
One of my game ideas is to make a game where you control Beavers making Dams to not let water in, a bit like the old game Lemmings.
Both my PCs can’t run Unity at the moment, probably because I downloaded the latest version via the Hub on Linux last night on the one at the Flat.
Anyway would I be able to make such a thing?
In your post you say your PCs can’t run Unity, but in your signature it says the opposite 
Well anyways, YES you can definetly make a game similar to Lemmings with Unity.
At the time both my PCs ran Unity 2019, now the Hub won’t load under Linux on Chrome OS.
Rich, I’m so confused by your posts sometimes. Sometimes you seem like you’re well on your way, and others as if you’ve not yet started.
The answer to any question of “is this game possible” is always yes. It’s possible. But if you’re asking, there’s a good chance you don’t yet have the skillset to do it at this time, and should continue developing and improving by doing smaller tasks first. Once you master those, you’ll know how to either start the game you want to make, or know what things you need to learn next.
One thing I’ll say for sure is that you should not post about game ideas. Not because people aren’t interested (Though, honestly… most probably aren’t. Everyone has game ideas.), but because doing so satisfies that need in your head that wants to make that game. Just talking about it makes you feel that sense of accomplishment, which actually discourages you from working on it and making it a reality. Trust me… I’ve fallen into this trap many times. I have game ideas I’m passionate about now that I refuse to tell anyone until I can actually show a prototype.
I’d encourage you to keep a gamedev journal or something to write down all your ideas, and then deconstruct them and break them down into small parts that you can actually start working on.
In other words… less talk, more work. 