Hey @Mykyta,
Unfortunately this is not possible. There are many feature requests around column widths.
I like your thinking though, and this could help as further feedback for the retool team.
If it were possible to access the width of a given column in the parent table, then it would be possible to dynamically set the same width to the matching/related column in the nested table.
Linking this thread to this other one (in particular to @emozio's idea which I really like) and tagging @AbbeyHernandez for +1's tracking.