This part is not as easy as you make it sound. You've invested man-days into figuring out the best software, settings, etc., to make everything work. I used to play around with ripping my DVD's and Blu-Rays using MakeMKV. Half the time it worked, half the time it didn't. The decryption keys didn't work, or some other issue. It's not smooth sailing unless there is a new method to rip your own media (which teeters on the legal/illegal front).Since yours is an extreme case (800 movies purchased & controlled by "strangers" in the cloud), I'll offer you what is- IMO-0 best solution to mostly abandon the Apple TV app and keep building your collection with actually owned, not lifetime* leased media.
Step 1: Get Big Storage for the 800 videos. That's probably one big hard drive. With 20TB hard drives available for as little as < $300 as I write this, taking possession of your library from strangers in the cloud is easy and cheap.
Step 2: Download the 800 from the cloud to your new local storage.
Step 3: Refer back to post #64 and do what is described there. This will index your 800 in the TV app on Mac (or iTunes on old macOS Mac or PCs) while leaving the library on the drive purchased in Step 1.
Step 4: Use the Orange Computers app instead of the AppleTV app on AppleTV to enjoy your movies. No more ads, no more services pitches, no more teasers to content you would have to buy/rent/subscribe for access, etc. Just enjoy.
...
Ripping your own video- just like ripping audio from CDs- will yield files you can enjoy in the Mac's TV app just like you enjoy the latter in the Music app. And both ripped video and ripped Music will flow to AppleTV Computers App via home sharing, where you can enjoy your 800 videos + future purchases, MINUS all of the promotional stuff that the AppleTV app slings in every open.
Otherwise, you can wait and hope Apple will someday get around to evolving removed features to being in there again. Maybe they will. Maybe they won't. But you have the power to adapt to an alt way today if you want it.
Also, Step 2 -- Download the 800 movies from the cloud? Don't those movies once downloaded have some digital protection in them? If so, are they really yours?
I'm not saying what you describe doesn't work, it obviously does for you, and I'd be interested in knowing more about how you do it. I currently have a Plex Server with around 500 titles and offers flexibility and a great experience. Also, Infuse for iPad and I can throw some movie files on a USB-C drive and watch them when away from decent internet.
So, if you care to share the best way to rip these days, many here might appreciate it.