Question one: is it used to train models?
This is the big one and the answer is frequently buried. "We may use your content to improve our services" is a sentence that can mean almost anything, and it usually means training. Look for an unambiguous statement that your uploads are not used to train models — and be suspicious of hedged wording, because hedged wording is a choice.
Question two: can anyone else see it?
Some products are, structurally, document-sharing platforms — Course Hero being the obvious case. Others are not. The difference matters: a platform whose business is a document library has an incentive for your uploads to become part of that library.
Question three: what happens when you delete?
Deleting a space should delete the files. Deleting your account should remove everything. If a policy only promises to remove your *access* to data rather than the data, that is a meaningful difference and it is a deliberate one.
Question four: whose material is it anyway?
Worth thinking about honestly. Your lecturer's slides are their copyright. A recording of a lecture may be governed by your institution's policy and, in some places, by law. Uploading them to a service for your own study is generally fine; a service that *redistributes* them is a different matter, and it may make you the person who shared them.