Mach3 can control the spindle via a relay or VFD inverter.
There are lots of VFD brands, and all the wiring to Mach3 is the same. Maybe terminal labels have different names, but with Manual, you can find the needed terminals.
Here I have a Mach3 red board, a 750 Watt spindle, and a 2.2KW VFD, and I am going to show you how to make them ready, wire them, and also config them.
This is a quick guide and demonstration with all the steps that I have done.
Nothing special, but it gives you a big vision.
Hpmont HD09 manual: https://drive.google.com/file/d/1Fxl7836Ufj_3Isr82em3nUwYBxhblKvP/view?usp=sharing
mach3 wiring diagram: https://drive.google.com/file/d/1wQoDQua_zCHgalmuWI6CfGSUlxVJR7Qb/view?usp=sharing
Music: Desert Music (https://www.youtube.com/watch?v=WQQmizjeBV8)