The issue with one-ingredient products is that it does not contain preservatives as such, so their expiration dates and PAO are short and I'd really avoid using them after expiration.
Luckily (?), in the case of the I'm from Mugwort essence there are preservatives but they're used early in the extraction process (if I understand it correctly) so they're not on the ingredients list.
Still, no one would dare to say it's safe to use expired products (the expiration date is not there for fun). So it's really up to you. Since there are no actives, the worst thing would probably be if the bottle got contaminated by something, then it could cause breakouts or irritation.
Also, I'm curious where did you buy it with such a short expiration (I hate it when sellers do this 😣)? I bought one last year from Wishtrend but it expires next year.