I followed the instructions in your video and my webpage does show all the data from the database. The text input does NOT filter the data. How can I solve this? I am using Bootstrap 4.3.1 If you like, I can send you the url.
I several issues on your page. 1. Why are these UPPERCASE? They must be lowercase, not sure why your DW generated them like that... : prntscr.com/od1vgp
2. Your GET parameter must only be lowercase and you must use the right GET param to filter. In your filter you use GET.filterJaar and on the page you linked your input to a parameter called JAAR??
all of your get params must be lowercase only. I recommend you starting again and make sure the GET param you use is lowercase, and it is the right one you use for filter and to link your form input to.