Moreover, if vacant - no rental or personal use - in my opinion considered Investment Property so the sale of the property be listed on Schedule D, and as someone referred basis would be Date of Decedent's Death. Also if Capital Improvements were performed and completed may have some additional basis.

Remember:

1. A capital loss may be limited by $3,000.00 per year if there are no other capital gains to offset the loss;l

2. Capital losses retains to the individual who sustained those losses until they are used or upon death;

     a. Might be good time for Tax Harvesting Profits from Investment Portfolios..

Also, Basis Version of ProSeries may not have the advanced worksheet ProSeries Professional.

Yet, a time I used "Inherited" in the cost basis of that worksheet - it threw the tax return into a dizzy with IRS Identification Department and took nearly 3 years of sending documentation! Yet to be "fair" happened around Covid-19 Era....   So lesson learn, at this point just use date of death and be done.

Well wishes to your client and you!