External Moritors connected to ipad only screen mirrors

So, there is some things you should try, but I have (almost) the same problem. What is most likely happening is somehow (provided your screen is full HD [1920x1080] and 16:9 ratio), the screen’s resolution for the mirror is something lower than 1920x1080. I have found that the display will not extend without the res. being HD (1920x1080) or higher. Another thing is that you must have a mouse and keyboard connected or it will not work.

Keep in mind that I have an iPad Pro 11” M2, but I hope it works for you!

-CPistol

While undocumented, testing has demonstrated that 4:3 monitors with a display resolution of 1280x1024 and below are currently only usable with iPad screen mirroring; as such, associated settings to disable screen mirroring in favour of Stage Manager are not available in iPad Display settings.

When used with a 16:9 widescreen monitor, with a native display resolution of 1920x1080 or greater, the full set of Display settings - and access to Stage Manager - should become available.

The iPad User Guide lists the upper resolution limit as 6K - but the Guide offers no lower limit, or suggestion of aspect-ratio, being a factor for compatibility:

Connect iPad to a display with a cable - Apple Support

This discussion thread may be of additional interest:

iPad Extended Desktop not working - Apple Community

In conclusion, your monitor must be capable of 16:9 widescreen 1920x1080 (FHD) to support Stage Manager extended desktop. Unless the monitor meets the minimum required specifications, you will not see the full range of controls in iPad settings.