If Settings > Sync > Core plugin settings is enabled, Workspaces (the core plugin) do sync and then download to other devices on my end.
I can open a workspace saved on desktop on my phone, but the open tabs are only the tabs in the first tab group (from desktop) and the mobile sidebars blank out. See:
If you open a workspace saved on one desktop on another desktop, it’s fine. Open a workspace saved on iPad on another iPad, it’s fine, etc.
The issue is when you try to open a workspace saved on one type of device on another type of device. I recommend labeling your workspaces per the type of device you save them on. e.g.
desktop--WS1
desktop--WS2
ipad--WS1
ipad--WS2
phone--WS1
phone--WS2