I think that, regardless of how you operated in the past, by your own admission it's not a business any more. I don't think you should file a schedule C, and you can't deduct expenses like the annual domain registration renewal fees or a home office. Since the domains are "property" you would report their sale on schedule D as capital gains property.
I tried to figure out if you could capitalize your carrying costs under section 266 and I just don't know. Most articles about section 266 focus on real estate, and while some parts of section 266 refer to real property, other places just say "property." But the tax reform law of 2018 also affected section 266. So the bottom line is I just don't know. You would have to get professional advice if you want to find some way to deduct your carrying costs.
https://www.law.cornell.edu/cfr/text/26/1.266-1
(For example, suppose you bought gold as an investment and paid someone to store it in a vault. Under the old law, the storage fees were a deductible expense as itemized miscellaneous deductions subject to the 2% rule. Your domain registration fees would have been deductible under the same theory, assuming you were holding the domains as investments and not able to deduct the expenses on schedule C. The TCJA of 2018 eliminated the misc itemized deduction. So now, the question is that when section 266 says "you can elect to capitalize expenses that would ordinarily be deductible" can you still elect to capitalize your carrying costs, or are they not eligible for section 266 because they are no longer deductible as itemized deductions. The IRS has not ruled on this question, apparently.)
