iPadOS 181.1 and display via HDMI

As described, you may have encountered HDCP...

HDCP (High-bandwidth Digital Content Protection) is just one of many DRM (Digital Rights Management) technologies designed to protect copyrighted video media from unauthorised copying.

Every component in the HDMI chain (source - such as iPad, AV processor/audio amplifier and display/monitor/projector) must be authenticated as supporting HDCP before content will play on the external display device. If any devices in the chain do not support HDCP, or their encryption keys have been invalidated, you’ll not have any video.

Not all streaming platforms enforce HDCP for all content, but many do. Some streaming Apps will not allow connection to any external video display.

Be aware that very few HDMI Adapters support HDCP. Unless the Adapter's specifications explicitly state support for HDCP, it is very likely that this DRM protocol is supported.

Apple's USB-C Digital AV Multiport Adapter does support HDCP:

https://store.apple.com/xc/product/MW5M3ZM/A

Having tested this specific Adapter with an iPad Pro running iPadOS 18.1.1, I have encountered no issues connecting to an external monitor via an HDMI connection.

Similarly, the Apple Lightning Digital AV Adapter also supports HDCP:

https://store.apple.com/xc/product/MW2P3ZM/A

While I have an iPad Pro with a Lightning port running iPadOS 17.7.2 - also without issues when using the Lightning Digital AV Adapter - I'm unable to update and test this iPad with iPadOS 18.x.

If you are experiencing issues with specific Apps, you would be best advised to seek assistance from the specific App Developer:

How to contact an app developer - Apple Support

We are not apple, we are apple users

You might want t give this as feedback to apple, please do so using this link Product Feedback - Apple