Custom field link multiple options depending on choice

So I am creating a custom form where I would like two Select fields with a list of options. Depending on which option is selected in Select Field 1, then Select Field 2 changes value.

How can this be achieved ? Perhaps Dynamic Link ?

Custom Script can be of help I guess.

and some discussions here:

Where you able to achieve multi selection option using select 2

I was not able to achieve this yet but I am still very interested.

Our Event form is becoming bulky because of the many fields necessary and it would help to have this development.

Our Events have many variables that depend on each other …