ipad lower brightness when i screen mirror or screen record

Have you tried this while connected to your Power Adapter? In addition to extending battery through dimming your screen, your iPad’s internal thermal protection will reduce screen brightness under heavy CPU/GPU workloads.

I see that there have been multiple reports of screen-dimming while screen recording. As such, either this is intended behaviour - or is perhaps a bug.

If troublesome, you might be best advised to seek assistance directly from from Apple Support.

Official Apple Support

Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

I provided a direct link to Official Apple Support in my previous reply.

You can also contact the Support Team using the Support link at top-right or bottom-left of this page - and as also suggested, you can initiate and manage your support cases using the excellent Apple Support App - for which a further link was also provided:

https://apps.apple.com/app/apple-support/id1130498044

To repeat the question - have you tried this while connected to your Power Adapter? You may find that you don’t see the screen dimming while screen recording…