Maybe. It depends on the rules of the program. It can be very difficult. You'd need to look for "upgrade awards" in the rules of whichever airline's miles you'll try to use for the upgrade.

Cash-equivalent programs - like ThankYou points that have a fixed cash value - are best suited to purchase domestic travel in economy class. Traditional mileage programs are better to redeem directly into premium classes of service on international routes.

In other words: if the cash price is low, use a cash-equivalent program. If the cash price is high, use real miles.

However, it can be difficult to earn enough in either type of scheme from everyday spending to actually redeem, which is why so many here focus on the sign up bonuses.

Then you can make a rational evaluation:

If I can get a signup bonus for 50k TYP, I can turn that into ~$650 of domestic travel or ~$650 of international travel.

If I can get a signup of 50k UA miles, that could be ~$500 of domestic travel or easily $1000 of international premium travel.

It's really in how you use each. Which is why so often people will ask: where do you want to go? how do you want to get there? it's very scenario-specific.