I have an M1 IPd Air, and I did install iPadOS 26 on it. The speed has been no issue for me, it runs fine. But for other reasons, I really don't like iPadOS 26.
Many of my complaints, relate to how it messed up my email in the Apple Email app (I can't stand the reoriginization and other changes), added the need for more clicks to do simple tasks, and I don't like the look of the icons, colors, etc, even beyond, that I never liked the so-called liquid glass. I did turn down the liquid glass effects as far as the settings would allow, so at least I can stand to look at it now. For these reasons, I have yet to add iOS 26 on my iPhone nor have I added it to my iPad Mini 5, which is still on iPadOS 18.x. I am not in a hurry to "upgrade" either of these other devices.