As of SingleStore DB Studio version 3.0.0, released on November 19th, 2020, Studio will not be compatible with the SingleStore DB Engine version of 6.7.
If you are currently running version 6.7, you can continue to use older versions of Studio. However, to use Studio 3.0.0+, you must upgrade to the SingleStore DB engine version 6.8 or higher.
Note that outside of Studio compatibility, SingleStore DB version 6.7 has reached its end-of-life, so it is recommended you upgrade to a newer version.