Since you have never depreciated the building as required you cannot use any DIY programs ... you need to find a local tax pro that understands the filing of the form 3115 with the 2021 return or you will pay much higher taxes than the cost of the professional. 

If you never took depreciation deductions on the property (to which you were entitled, and actually obligated, to do), then you need to file Form 3115.

See https://www.irs.gov/instructions/i3115#idm140516454129840

This particular form is not exactly a DIY project so you should seek guidance from a tax professional.

You will need a tax professional to assist you in reporting the sale since no depreciation was taken in 20 years.  This is not something you can do with a DIY tax preparation software program.

Technically there is no requirement to file the 3115 so you can get the benefit of the depreciation you didn't take over the last 20 years.  however, the tax laws still require you to compute the gain and thus the taxes on the sale as if you did. without the 3115 you can't take depreciation in the year of sale. so see a pro.