Illustrator 23.0.2. I use "cm" units in whole software, but Distribute Spacing right now working only in points...
I think your software is falling down year by year.
The distribute spacing value still gets stuck in points. September 24, 2020. This bug was also documented at https://community.adobe.com/t5/illustrator/align-to-objects-unit-change/m-p/11053672?page=1.
As of April 21, 2020 this bug still persists over a year after the original report. Seems like it would be a simple fix...
This same issue has also been described at https://illustrator.uservoice.com/forums/333657-illustrator-feature-requests/suggestions/37523554-distribute-spacing-in-align-tab-uses-wrong-units.