Welcome to the community, @Gesa_Kotter! I’d be inclined to solve this problem using an automation that runs a script. The tricky part (aside from writing the script) would be the automation trigger. How are new records created based on these social media comments? Do you have other automated systems that create them from the various social media channels, or is there manual input as part of the creation process? If it’s the former, it’ll be a lot easier to set up a reliable trigger.
One way to optimize the searching process (also something that this same script could handle) would be to create a
[Users] table, where the script records unique users. Searching through that table—or, more likely, a specific view on that table that only shows users from whichever platform a new comment came from—would be far more efficient than searching through all records in the main table from incoming comments across all platforms. The script could link each new record in the main table to its related user account if found, or to a brand new user account if not found. You could then create a count field in that
[Users] table that tracks the number of incoming links from the main table, and roll up that count back to the main table, which would tell you instantly if someone is new (only one linked comment) or a returning commenter (more than one).