Sounds like you’re nearly there! I probably didn’t explain this very well, but the route you need to add manually to LAN devices (192.168.10.10 in your case) is actually the route from the physical LAN to the ZeroTier network. Although you’re trying to reach 192.168.10.10 from the ZeroTier network, at this level the return route is required for a connection to be established in either direction.
If you let me know your ZeroTier network range I can give you the exact command you need to run on 192.168.10.10, but assuming ZT is 172.27.0.0/16, you would run:
route -p ADD 172.27.0.0 MASK 255.255.0.0 192.168.10.11
If the 192.168.10.10 device is not a Windows box, then you might need to work out how to add a static route to it and translate the above into whatever command line/GUI you use to administer it.
Hope this helps!