Today I got a notification for an update to Sidesync on my Win 10PC. Post installation a dialog box appeared saying Sidesync is not supported by the Galaxy S9 and S9+ and instead a future version of Samsung Flow will replace it.
I just tried to load Sidesync & the message you mentioned loaded, so I headed here.
You can get a USB Bluetooth dongle for like $10 if that works for you. I plugged one into my PC. Works fine.
I'm not sure why they wouldn't have it where there would be continuous coverage. Don't get rid of one before the other is finished.