For US machines, synchronous tapping is standard.
For overseas machines, synchronous tapping is a paid option.
F79 changes the way G84 works. If you change this, you will cross thread because one is synched and the other setting is not.
Just use G84.2 instead which is always synced and don't worry about it anymore.... check it in a test block if you like.... Also, you still need to follow the basic rules. for example, if you change anything related to the Z start point (i.e.: tool length, R plane, work offset, etc), then this will also cross thread your holes.
It's just a part..... cutter still goes round and round....