It may have been residents only in the past but that link says starting from Jan 1 2022 it is available at a fee for tourists. Typically, the vaccination check is part of TT but I am not entirely sure how it works for tourists. The TT safe entry/vaccination check is required at hotels so that is a potential issue if arriving late at night and can't get the token until the next day but may be some way around that. Renting a mobile phone at Changi with a local sim card may also be possible and is suggested in the safe travel FAQ but i am not sure about the specifics.