Hi cohara1103,
welcome to this Apple )user-to-user) community!
Re: It use to be simple to use my ipad with my left hand didn't need my prosthetic. I could read change pages Flip through photos sent by family change music it was simple. Now with all of these "features" it's impossible without putting on that prosthetic.
Commiserations on the ever-changing tech. conditions you face.
Seems we are often needing to find new ways of doing things.
With iPhone there is a "reachability" setting the helps with using one hand for operation ie: it lowers the top of the screen so that all is within easy reach for the thumb. Yet it seems you need much more than that kind of assistance.
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Re: iPad, iPadOS 26 : Is there a One hand set up?
Am no expert in this area, and I don't know of any one-hand set-up.
Yet your question to the community certainly deserves some response.
There are now other ways to operate iPad than with one or two hands,
You may want to explore some of those possibilities:
Accessibility features for mobility on iPad - Apple Support
Eg: says:
With built-in accessibility features for mobility, you can navigate and interact with iPad using just your eyes, spoken commands, assistive devices, an external keyboard, and more. You can also set options so it’s easier to use gestures and press iPad buttons.
To explore accessibility features for mobility, go to Settings 
> Accessibility, then scroll down to the Physical and Motor section.
The Linked article above provides more info. on each available setting:
Apple also provides an Accessibility Support Team. You may want to reach out to the experts there for their advice: See: How to contact Apple for help with accessibility features - Apple Support
All the best :-)
