It doesn’t matter which font it is… all of them look bad - I just put here Arial so you can see the difference between emC and another client
So you have Win11 and it looks good on your computer? Can you share some screenshot too? (ideally with “WeTransfer” text)
Just classic settings, nothing special:
Well no, I wish I don’t have to solve things like this and it will work automatically so I don’t need any super extra settings then… but unfortunately it is like it is
I would put here full screenshot of the app and you will see how ugly it is, but i don’t want to expose all my emails 
One more thing: I’ve tested it on another computer with Win10 and there is the same problem, so it looks like it’s simple some problem in the app source code