Furthermore, require dashes over slashes to signal that you are expecting ISO-8601 compatible dates, i.e., YYYY-MM-DD. Most users does not know the standard even exists, but it serves as an affordance that it is different from dd/mm/yyyy, etc.
https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...
or a text field with some code that converts vernacular dates to a structured format. I don't think users are going to be too weirded out at seeing "1997-04-15" and will probably learn to use that natively.
The hard part is that a lot of devs aren't aware that there's a standard and that standard is superior to the alternatives.