Well, if the truck was fully depreciated, then it had a cost basis of $0.00.  Therefore, whatever the amount the insurance company paid you (the proceeds) would be a capital gain, and taxable.  

If you are Married, filing jointly,  and your income is $0 to $80,000 - your long term capital gains tax rate is 0%.

If you are Married, filing jointly,  and your income is $80,001 to $496,000 - your long term capital gains tax rate is 15%.

If you are Married, filing jointly,  and your income is $496,001 or more  your long term capital gains tax rate is 20%.

You have to go to where you enter the business income and expenses and then look for Business Vehicle Expense and find the screen that says Tell us about your business vehicle. There will be an option on that page to indicate that I stopped using this vehicle in 2020. 

Choose that option and you will be prompted to enter the selling price, which would be the insurance proceeds, as well as some other information and any gain or loss will be calculated.