Yes the US economy is growing. GDP is the market value of all the produced goods and services. If it grows, it grows. A growing GDP means that someone consumes more (not necessarily everyone). The economic gains for some are real.
Now the thing with the deficit. The US government is partly borrowing money to finance its operations, huge amounts of money. It could increase taxes instead or cut the budget both of which might influence growth negatively, but the interest rate that the US government has to pay on government bonds is quite low and in some other countries currently even negative. What do you do if people want to throw money at you? You take it. The deficit spending in the US can continue for some more time while the overall debt level is still not regarded too high.
At some point investors may lose faith in the US dollar and switch to other currencies or a future US government could decide to prints lots of dollars to pay back creditors, which then results in some kind of inflation. Then a lot of gains made now could prove being only temporary. We have to wait and see how it all works out in the long run.
In general, you would have to look at the overall debt, government and private and commercial. And you would also like to look at inequality because who cares if the upper 1% earns much more while real wages are stagnating for the lower 50%? Unequal economic gains can be losses for many.