SUMMARY
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Neon Unstable Plasma 6 Beta 2 at 29 Dec 2023 still does NOT have Display Auto-Rotate option
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The screen Auto-Rotate option would make Plasma 6 ideal for Tablets, like the MS Surface Pro, or for 'Convertible Laptops' like Lenovo Yoga and some HP and Dell systems (for example).
Note **   Some other Linux Distros have this enabled by default, Mint Cinnamon for example has the required software installed and the options is in Settings > Display Configuration

STEPS TO REPRODUCE
1.  Hold Tablet or Laptop in Landscape Orientation
2. Turn Tablet or Laptop to Portrait Orientation
3. 

OBSERVED RESULT
Nothing happens

EXPECTED RESULT
Screen adjusts to diaplay in Portrait mode

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version:   KDE 6 Beta 2  at 20th Dec 2023
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
Running default Wayland Session

REQUIRED FIX:
Running    apt-get install gawk iio-sensor-proxy 
(for those of us who know how to do it and what to install)
Then rebooting fixes the problem and adds an entry in Systems Settings > Display Configuration  
After reboot that allows Automatic Orientation to be toggled ON or OFF

And the rotation works perfectly.

Steps to swat this bug:
Worth Trying :
Have       gawk and iio-sensor-proxy        installed by default !

Variations of this problem have been filed for years.  We are seeing more and more of these dual-purpose devices coming onto the market, especially now that a powerful 'used' MS Surface Pro or Lenovo Yoga can be had for about $200

Both gawk and iio-sensor-proxy are already in the repos.  It is a dead easy fix and it would make a lot of people happy it it was working when Plasma 6 is released.

Last tested 29th December 2023 on Kde Neon Plasma 6 Beta 2
Was also not working on Beta 1 or on the Beta 2 upgrade

I also tesated it in Kubuntu, where it also didn't work.
I know it is partly a duplicate bug - but having those two packages installed by default might go part of the way to solving it.