Can I re-size table cell width?

Questions should provide context, or they can’t be answered.

Ok, so you’re referring to the new editor and its options.
Tables are difficult to style as a whole, and trying to do each column or row is out of scope for the editor. I think each block has a 3 dot menu, where you can edit the HTML for the block. Perhaps you can add a class or even a width attribute.
You have to remember that the theme will be styling the table and including (or not) the editor’s block styles.

If a table has table-layout: fixed, the browser uses the first row to set the widths of the columns. If not, the browser tries to make it all fit.