Can I download Minecraft if I have it on the Switch?

I have Minecraft on my switch and I'm logged in there with a microsoft account but now I want to have the game on my pc / laptop as well, but there's only something that says if I already have Minecraft I should log in with my Mojang account

You will have to buy Minecraft for PC again. You can choose between the Java and Bedrock version. The message you mean just indicates that if you should have bought Minecraft for the PC, then you can log in with the Mojang account with which you bought it

Nope you have to buy 2 different games

Unfortunately you have to buy Minecraft on your PC