I hope (for your sake) that you don't have any users that can invoke their GDPR rights against you by virtue of their citizenship.
For the sake of incentivising companies to do the right thing, however, I hope you do have some EU or UK citizen users who do litigate or have their data protection authority investigate and formally punish Triplebyte, even if only to establish clear precedent here for the future.
https://www.hipaajournal.com/does-gdpr-apply-to-eu-citizens-... seems to suggest it is based on location. There would seem to be standing for anyone based in Europe that made an account when considering a move to the US, or who is based in Europe next Friday when the "data processing operation" occurs. That seems like it would give them standing, even if they weren't protected while overseas, as this is a new data processing operation.