Here's the link to the similar question
https://salesforce.stackexchange.com/questions/306284/how-to-filter-data-in-datatable-lwc-based-on-the-input-in-search-bar/370164#370164

The above works fine with non-lookup fields but doesn't seem to be working in my case.

Edit : If I use regex.test(row.Name), I'm able to search the records based on Name column however, one of my columns has fieldName: Owner.Name and the search isn't working.

.js code snippet:

    updateSearch(event) {
         var regex = new RegExp(event.target.value, 'i')
         this.data = this.testSearch.filter(
            row => regex.test(row.Owner.Name) 
        );

Any idea on above?