You are correct. Long-term losses will be netted with long-term gains and reduce the net long-term gain. You don't have any choice about how gains and losses are calculated on your tax return.
I can only think of two possible ways to get around this, and you might not be able to do either. One is to find some short-term losses that you can take in 2021 to offset the short-term gains. The other is to postpone the short-term gains and long-term losses to 2022.
One other caution - Tax laws can change. The treatment of long-term gains could change. It's even possible that changes could be made that affect 2021. And it's certainly possible that there would be changes for 2022.
