Starting with the release of Strategy ONE (March 2024), dossiers are also known as dashboards.
Steps to reproduce:
1. Create a new dossier and add a Grid visualization.
2. Add three metrics.
3. Trying to change the size of the columns is impossible.
Action:
This is a known defect in Strategy Web and is being reviewed by the Technology Team.
Workaround:
Change to column size to “Fixed” and modify the value. After that modifying the width by dragging the line will be possible again.

Affected versions:
2021 U4.1., 2021 U5, 2021 U5.1.