Symlink support on Insync 3 works via Local Selective Sync. Thank you @F_M and @bnpndxtr01 for bringing this up!
Could you please email your logs.db and out.txt files to support@insynchq.com with the link to this post? Those files can be found by clicking the 3 dots on the upper right > Help > Open logs.
We’ll look into this!