I created a ui only field (multi-picklist) and added it to the table as a filter, but it is not doing anything, although request is going to the server and fetching the request again. It would be helping if I can get the value of this filter/field just before the request goes to the server, so I can set this value to a condition and table can fetch the filtered records.
UI-only fields can be used to show and manipulate data client-side, after the model has loaded and without having to save values to the datasource. Because of that, they only stay with a model until the model is queried again. Filters on a table work by adding a condition to the model and then querying the model, so UI-only fields won’t work with filters. Here’s a tutorial on what you can do with UI-only fields, if you’re interested.
What do you want to accomplish through the multi-picklist filter? Would it serve your purpose to create a multi-picklist filter based on an already existing field? If you need more control over the filter you also have the option to create a filter with a manual source, where you pick what conditions the filter affects.