Turning off a parked domain doesn't affect the domain reputation at all, in fact, parked domains are pretty much ignored by Google and are not likely to appear in search results because they do not provide any value to an end user.
Once you set a real website in the domain it will start getting indexed.
Search Console support confirm this:
parked pages don't provide value to searchers, so we don't typically
return them in our search results. If you have parked domains,
activate the domains and fill them with useful content to make them
eligible for being indexed and returned in search results