You're entering something wrong, or incorrectly selecting/not selecting something you should in the program. That comes as no surprise, because the program itself is asking you for incorrect information on one of the screens. The information asked for is incorrect only for your specific situation.
The program "does" figure the depreciation correctly when you enter the correct data and make the correct selections. At least, my desktop/CD version of Home and Business does. One thing to point out is that for those who are renting a portion of their primary residence, there is a screen where one of the questions is worded wrong for "that" specific situation and only "that" specific situation.
As you work through the asset, you have a screen titled "Tell us more about this asset". On that screen select "I purchased this asset new" and select "no, I have not always used this item 100% of the time for this business." Then select "I used this item for personal purposes before I started using it in this business".
Now here's where the disparity is. For you the "date I started using it in this business" will be 1/1/2020 of course. But the next entry, "Percentage of time I used this item for this business in 2020", would be correct to answer 100% in your case if you had converted the entire property to a rental in 2020 with a conversion/in-service date of 1/1/2020. But for you that question should ask "percentage of floor space used in this business in 2020". If you enter 3.19% in that box and click next, your first year depreciation will be darn near spot on.
Here's how it works manually, per the IRS instructions.
Using the IRS worksheet on page 38 of publication 946 at https://www.irs.gov/pub/irs-pdf/p946.pdf
Depreciation period: 27.5 years
Cost basis to be depreciated: $245,000
Business/investment use: 3.19%
Adjusted cost to be depreciated:$7,815 (thats 3.19% of $245,000)
Depreciation period: 27.5 years
Then table A-6 on page 72 applies to you. Since you placed the property in service on 1/1/2020 you multiply your adjusted cost basis of $7,815 by 3.485% and you get a first year depreciation amount of $272.
