I know that everyone has been waiting a long time for sync and I want to reassure you that it is high on our list of priorities. As users of Squid ourselves, it’s something we really want as well! We appreciate your patience.
This is something we’ve been investigating since the app’s inception and we continue to investigate constantly. Syncing is a very difficult problem to solve, especially with regards to handwritten notes which can be combined with images and text and contain backgrounds from multiple PDFs. I don’t have an ETA for when sync will be supported, but rest assured this is a high priority for us. We appreciate everyone’s feedback on this idea.Hamza Ahmad commented
I don't think the developers even care. It's been almost six years since feature was requested. Almost everyone wants this feature. I am a developer. I know that adding a sync option cannot be that difficult. OneNote has it. Very disappointed. I am switching to OneNote and the only reason I am doing this is because of no synchronisation. I loved squid but the lack of synchronisation has made me kinda hate it now.