"°C" as symbol in font?

Could you clarify what you mean by ""°C" as a vertical symbol"?

Do you mean something like this (with °C as a superscript?):

10^°C

Garmin doesn't show available characters in the UX guide anymore, but in the past they've indicated that the ° (degree) symbol is available for both number and regular fonts, for many (but not all) devices, including Edge 1000 (not sure about Edge 1030 Plus, but I assume so)

So if you have a simple datafield (which just returns a value -- you don't control how it's drawn), you would include the degree symbol as part of the text that you return in compute(). But then all the text would be the same size and have the same vertical alignment.

If you have a complex datafield (which gives you complete control over what the field draws), you would draw some text that includes the degree symbol. In this case you could make the "°C" text smaller and higher than the temperature value (like a superscript), if that's what you meant.

Only caveat is that you'd want to test it in the sim for all supported devices to make sure they can all display that symbol properly.