Prevent submit button being disabled when req fields

I’m working with a theme in which the submit button is initially disabled when the form has some required fields.

Also, when I check a checkbox, all previous (above it) required fields if present, trigger the error message below each one if they’re still empty.

I don’t know if this is a built in behavior or a custom one, but I’m not finding a relevant JS snippet which triggers those.

If it’s a built in one, is there a way to control it? eg, disable and only perform the required checks upon submitting the form?