According to Ignoramus2331 :

This is great. I have existing conduit going into my basement
"workshop". It supplies 110v right now. I want to rewire it to supply
20A 220v, with neutral, and will add 110v outlets on both legs, as
well as 220v outlets.

On the main panel, I will use a double pole 220v breaker so that ``all
ungrounded conductors of the multiwire branch circuit are opened
simulaneously by'' that breaker.

The reason for it I want to convert my drill press to three phase with
VFD, mostly for tapping. I need 220v for it.

Also, on the same circuit, outside the basement wall, I want to add
outdoor receptacles (110v and 220v) for my pool's pump. It would be
GFCI protected and I will use outdoor rared hardware.

The above mentioned pump runs a water slide on my inflatable round
pool, which also doubles as a water filter.

That sounds _way_ more than can be supported off a single circuit,
240/120 or otherwise. You'd be better off running multiple circuits,
some dedicated 240, others 120. Or put a subpanel in the basement
and do it from there.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.