A friend who has limited eye sight would like an audio recorder on his Samsung phone. Ideally it starts when he long presses the display anywhere after unlocking the phone.
Is that possible?
I'm thinking there are at least 5 good approaches to help out your friend:
Take a close look at Android's and Samsung's accessibility services. I haven't had the best experiences with Samsung devices, but some of the accessibility services they offer are top notch. If you go into Android's Settings UI, you can explore. You may find something exactly like you describe, or something else that you can adapt to your friend's needs.
Use a custom launcher like Lightning Launcher, Total Launcher, or Nova Launcher, and configure the entire main home page be one huge button that, when pressed, launches an audio recorder of your friend's choosing. I've used all of those launchers, and Lightning Launcher is by far the best and most flexible, but it has a significant learning curve. Total Launcher is also very flexible (yet not as flexible as Lightning Launcher), but its learning curve is quite steep. Nova Launcher is the easiest to configure, but the least flexible, by far.
Using any of the aforementioned launchers, you can program a swipe gesture (e.g. 2 fingers swiping up) to launch an audio recorder of your friend's choosing.
Install HomeBot from F-Droid and remap the home button long press on to launch an audio recorder.
There is a great open-source app that allows you to reconfigure all the physical buttons on your Android device called KeyMapper. You can configure it to start an audio recorder when your friend presses or long-presses a button.
Note that for options #1 and #2 (and perhaps for #3, #4, and #5), if your friend prefers, they can link directly to the activity within the audio recording app that begins the actual recording. That way, the recording starts right away.
The biggest challenge I see is for your friend to know that recording is taking place. This partially depends on the limits of their vision. One tip is to enable a sound when the device is turned on. Most modern Android phones have this option, often tucked in with the other accessibility settings.
I admire you for being willing to help others. Good luck!