Where are you seeing that fr isn't supported with grid-column?

Are you testing on J4 Alpha 2 or Nightly?

Can you provide a screenshot?

\templates\cassiopeia\css\template.css (starting line 10166)

.container-component {
  /* autoprefixer: off */
  grid-column: auto 2fr; }

\templates\cassiopeia\scss\blocks_css-grid.scss

.container-component {
  /* autoprefixer: off */
  grid-column: auto 2fr;
}

I see the message, that there is an invalid value for property grid-column, too

I use the current 4.0-dev branch.

Attached you see a screenshot.

A valid issue. That entire rule can be removed.

I was waiting for a decision on #19062 which rewrites the grid and removes that rule.

BTW, still exploring the fact that featured articles or category-blog are not displaying more than one column is related to CSS grid or else.

Maybe you are looking for this... #18319

@ciar4n
Tks for the update.

#18319, very interesting proposition. Unfortunately, and to my dismay, "masonry" disappeared from /media/vendor/ even though mentions of it still exist in current cassiopeia's template.css.
Looks like you deleted this in #19062. CSS grid or flex don't render exactly like masonry.
I didn't post on the issue of columns not showing in featured articles or category blog because I guessed it was a work-in-progress.

#19062
I will test it as soon as I can.
To gridify a template is not an easy feat. Kudos.

Set to "closed" on behalf of @Quy by The JTracker Application at issues.joomla.org/joomla-cms/19476

Please test PR #25256.