Hello @irfanz,
Welcome to Plumsail Community!
You can change the width of the multiline text column in List or Library control using the CSS.
First, add a CSS class to List or Library control, e.g. my-table.

And add this code to CSS editor:
.my-table .fd-sp-datatable tbody tr td:nth-child(3) {
min-width: 1200px;
}
Where 3 is a number of a column. The count of columns, in this case, starts from 1.