iPad 1st gen 2nd monitor
Can I use my IPad 1st gen as another display for my 2021 MacBook Pro?
MacBook Pro 14″, macOS 12.6
Question marked as
The original iPad does not meet the requirements for SIdecar
Use an iPad as a second display for a Mac - Apple Support
It also does not meet the requirements for Duet
https://apps.apple.com/us/app/duet-display/id935754064
The original iPad is only 32 bit whereas all app for many years have only been 64 bit.
Conclusion is NO.