Disabling the "Length Authoring Tools" (css unit selector) in Chrome Devtools Inspector

Solution 1:

Updated answer 2021-11-16:

An option has been added to disable Length Authoring Tools in Chrome 96.

The following is mentioned in the official release notes for Chrome 96.

To disable Length Authoring Tools, navigate to this location in the DevTools and uncheck the checkbox:
Settings > Experiments > Enable CSS length authoring tools in the Styles pane.

But...

The main issues regarding Length Authoring Tools have also been fully remedied in Chrome 96.

The initial incentive to disable these tools has been greatly diminished because of this.

A chevron will now appear to the right of the hovered value instead of reacting to clicks to the entire unit portion of it.

Copy paste now also works as intended.

Conclusion:
It is now possible to disable the Length Authoring Tools, but you might no longer need to.

Old answer:

You can't.

(Though fixes are coming!)

Fixes have been added to Chromium ( [1], [2], [3] ) that are slowly making their way to the stable release of Chrome.

But help is on its way...

Chrome 96 is scheduled to be released on November 16 2021 (source), or ~3 weeks after October 28 according to this official tweet. It will at least contain a revert to free text editing of css properties (source). Hopefully version 96 will address the issue completely, but if it doesn't then the next major release is scheduled for January 4 2021 (If this issue is unresolved by then somebody at Google should be fired).

As for now, Chrome Canary seems to have these fixes implemented and might be considered an alternative solution to the issue if you find the current state of Length Authoring Tools unbearable.

Please be advised that Chrome Canary can be quite unstable.

This question and answer will be edited and corrected once there are real fixes in the live stable version.