can still claim it as an expense (not depreciate it) in the year 2021 if I use the De Minimis Safe Harbor.
Yes, provided you actually paid for it in 2021, and can prove it if audited. (slim chance of an audit, but not zero)
Even though the apartment was "not for rent" during renovations, those are still considered expenses if I did NOT intend to change the purpose of the rental property.
Yes, they are still valid rental expenses. Just because the property was vacant, and since you did not have any personal use of the property during the vacancy period, the classification of the property does not change, and remains as "residential rental real estate". So even utility bills you paid during the period of vacancy are deductible rental expenses.
Please allow me to clarify a few things, mostly for others reading this thread, with some hypothetical concerns, which you did not post.
But I was basically living in the property for a few weeks, doing the labor myself. Is that personal use days?
No. You were not staying at the house as your primary residence, 2nd home, vacation home, or any other personal pleasure type of use. You were there for the primary purpose of "doing the work". So those days/night you stayed/lived there are not personal use days.
But while I was there doing the work, my spouse and kids stayed also for a bit of vacation time while I did the work.
Now you have personal use days since the property was used by the family as a vacation home during their stay. When you enter the personal use days in the program, all of your expenses for the entire tax year will be prorated and adjusted accordingly, including depreciation.
