We purchased a timeshare in 2021 and didn't use it for personal use. My understanding is that we can treat the timeshare as either a second home or investment property?

Yes, a time share can be considered a second home, however, unless you are paying interest on a loan for the time share you will not get a deduction for the fees paid. 

When you sell the timeshare, that is when you would enter it as sale of home or investment property depending on how you treated it. 

Thanks!  If I classify as a real estate investment, I should be able to deduct any maintenance fees in the current year though, correct?