Most probably this is correct. One can say the same about most enterprise targeting offers, for example by Microsoft.

People who consider it for private usage should make decisions knowing such details.

Disclaimer: this is a personal impression/thoughts, I could be dramatically wrong here.

Usually not foss and rather expensive.

Note about deepl: according to their EULA they collect all what you type there and use it for training their algorithm. They are much smaller that Google and co, what makes me thinking that your data could be more “visible” in the training results.

The service as such is good, though.