If you weren't collecting that info to begin with, you can't view it after the fact.
Do you have "Keep track of who edited the data" enabled? If so, this will give you a name (though the column may be hidden).
I checked our activity report and noticed the updates were done by a strange client id using an IP address that was nowhere near my location. I submitted a report to Esri Product Security Incident Response and they confirmed the client ID is from Microsoft Power Automate. This makes sense as power automate uses a webhook attached to this survey. The web hook shows that it was modified, which was the same date and time as the last modified date of the form item. I'm not sure what it was modifying, but this seems to make sense.
Yep, that makes sense.
If your Automations are consolidated to a single account, it should be relatively easy to track down the flow. If not, you may need to play telephone-tag to figure out what is going on.