How to set up subscript or superscript in data format in Numbers

I see subscript and superscript in Format>Font>Baseline are disabled for custom Data Format.

But, there is an alternative for putting supurscript/subscript digit.

1. Set the cursor to the position where you want to put superscript/subscript number.
2. Open "Show Emoji & Symbols" from the Input Source menu.
3. Choose [Digits] on the left side pane.
4. Double click the character to insert to the cursor position.

Not all characters, but some other character are also available for subscript and superscript.

On the Emoji&Symbol table, type in "superscript" or "subscript" in the search field on the top-left.

You'll get list of those character under "Unicode Name"

Grad to hear your problem is solved.

I should note that it need to set up some preferences to make the menu/items available, if not configured yet.

I believe you already figured out, but let me put it here for later reference.

Show Input menu

In System Preferences>Keyboard>Input Sources,

Tick on "Show Input menu in menu bar"

Show Emoji & Symbol

In System Preferences>Keyboard>Keyboard,

Tick on "Show Keyboard, Emoji & Symbol Viewers in menu bar"

Digits on Emoji&Symbol table

Switch to full view by clicking the icon on top-right of characters table.

Choose "Customize List..." in the gear menu ( near top-left corner ) on the Emoji&Symbol characters table.

Tick on "Digits" in Symbols group ( and others if you like )

# "Unicode" in Code tables group is useful in some case to see all characters available on the system. [IMO]

Click [Done] button.

The search-by-keyword method works even in compact view.

You can enter superscript and subscript here (under Advanced Options > Baseline):

SG

perhaps you can post a screenshot showing what you have and what you want. I do not understand phrase "so that I get the m3 correct"