Have specific Calendar days/dates be disabled (example..Past dates)

You should have at a minimum the ability to prevent the user from selecting past dates. It would also be even better to also allow disabling of certain days and specific dates.

Here is a link to an implementation that might be of interest to you in this regard: https://www.peeayecreative.com/docs/divi-contact-form-helper/date-time-picker/

They have addressed the issue not only at a date level but done so at the level of time.