It was possible to send a form selecting "other" in One Choice, but nothing writtin in the field

Example:

What do you like?

()apple

()banana

() _____

SEND

What do you like?

()apple

()banana

(X) _____

SEND!!!!!!!!!

I dont wanna this field in blank, I wanna make an obligation

THANKS!!!!

If you do not want the other option to be submitted empty, you just need to require the field:

Result:

Let us know if you need more help.

But even if the field isnt required, I can select this one and write nothing.

Correct, because unrequired fields can be submitted empty. So, to avoid empty fields, you need to require them.