Hi @lex_zap,
Welcome to the Community! I hope I can provide some info regarding suppressed profiles and winback flows.
If you were to suppress or add any clients to your suppression list and these clients later subscribed through your form and / or made a purchase, they would be automatically removed from the suppressed list and move back to the original list they subscribed to.
The same would apply if the client was suppressed manually. Whenever someone unsubscribes, they become globally suppressed in Klaviyo. However, contacts can re-subscribe and be re-added to your list at any time. But unsubscribed and suppressed profile will need to resubscribe to be unsuppressed. If you manually upload their profile information again or they resubscribe to a list via another source, such as a Facebook lead ad or some 3rd-party form tools, they will not be marked as unsuppressed in Klaviyo and you will not be able to email them.
Here is our resource link that discusses suppressed profiles - About Suppressed Profiles in Klaviyo
This link may also be helpful when looking at the issue of unsubscribing and resubscribing.
If at some point you decide you want to revert a suppression on any client, and remove them from suppressed list, you can always look at the clients profile in the Profile tab to view their activity and to be if they are globally suppressed - Guide to List Cleaning.
Additionally, here are some Community posts regarding winback flows I would recommend to you!
Thank you and have a good day!
Alex