Is it possible to upload to multiple data fields using a singular multiline input? in other words, break up information in a multiline input?
Yes, but really depends on your use.
I have a multiline input that accepts text values and the user is instructed to add them on separate lines. I then take that and create a list of texts.
Is it possible to update a list of users instead of creating a list of text?
Possibly. I haven’t needed to so have not thought through the process. My assumption is that whatever value you have in the multiline input can be applied to multiple users, so just use the workflow action to modify a list of things.