Unexpected tax bill due to poor decision making by financial advisor

My dad died in 2020. He lived abroad and wehn he passed it turned out one of his us banks decided to freeze his brokerage account until they received some letter from the irs. His broker turned that account into cash explaining he didnt want to see the market crash and we are unable to do anything about it.

I agreed bc at the time I knew absolitely nothing about any of this.

Now I am finally getting around to doing dads taxes and the bill for 2021 is like $16000 bc of capital gains from this move. If i knew then what i know now i never would have let the broker (my now deceased uncle by the way) do what he did.

Do I have any recourse - are there moves i can make to lower this bill, or anything? And yes I know I dropped the ball on the taxes- so please go easy on me with the shaming. I have that all covered.

Thanks!