Hello,
No, it doesn't have any hard limit enforced. However, due to how end-to-end encryption works, you might face your devices performances limits as the number of users goes up.
Each change to the document has to be synchronized in real time with everyone, it's quite resources hungry. People with less powerful devices (like cheap smartphones) will likely be the first ones to experience a degraded usage. Changes made to the document will be slightly delayed, introducing some "lag".
No worries tho, I have no idea how many person you want to collaborate with at the same time on the same document, but it'll should support a fair amount of collaborators without issue.
Hope this helps!
