capitalizing interest on investment property only applies to unimproved and unproductive land (IRC 266) and in cases of construction period interest for long life assets (IRC 263A)
to elect IRC 266 a statement must be included with each year's timely filed return.
if significant $$$'s are involved you may want to confer with a malpractice attorney.
however, perhaps your accountant didn't take the deduction because they used the stndard deduction for that year which exceeds what your itemized deductions would have been.
hopefully, you extended 2018 otherwise it's too late to amend since an amended unextended 2018 return was due by 4/15/2022
