It's a spectrum. I don't think that they will be able to sell t-shirts using a drawing you've uploaded. But it will probably allow them to defend themselves a bit better if they get sued for selling the data for LLM training.
You can't give up the right to sign your work with your name. But you can definitely share rights to reproduce your work etc — although perhaps not in a clickable EULA.
In Austria and Germany, you just cannot transfer the copyright ("Urheberrecht"). You can only transfer - meaning sell - the right of use ("Nutzungsrecht"). The only exception I know of is with employments, where the employer is the rightful copyright holder. The US, Switzerland, and maybe other legislations allow for the transfer of copyright.