Is it possible to put in laptop memory DDR4 2400mhz if the strap is already DDR4 2133mhz?

Before you could. Just both modules will work at 2133. I do not think that something has changed. In the extreme case nothing will explode. Just laptop won't start.

Very informative question.
Given that You give it, even if for the money, take the test. It would be great to read first BOM to mothers and so forth, but You're not going to the store...in the worst case does not start in the best work, timings and frequency if I remember correctly are at the lower end of the worst.