[Magisk] J.Michael:
It wasn't "System as Root" that forced us to install Magisk in recovery, it was the supposed lack of support for a ramdisk, which is (mostly) the thing Magisk actually patches. There are threads on Samsung tablets where people say they have succeeded in patching the boot image. The usual advice is if the Magisk app says "Ramdisk: Yes", then you can patch the boot image. If it says "Ramdisk: No", then you can try to patch the boot image. If that works (meaning, you flash it and it boots and you have Magisk), great. If not, install in recovery.

Installing in recovery for the rest of the world means having to check a box that says "Recovery" in the Magisk app when patching an image. For Samsung, Magisk patches the AP.tar file, which means it patches three image files within the AP.tar file. If you are offered a checkbox "Recovery", you should check it. There is a chance that Magisk just decides to patch recovery and doesn't offer you a checkbox.

You're not using the recovery boot image to boot the Android system. If Magisk is installed in recovery, then when you boot the recovery image, Magisk gets control. To give you a way to get to the actual recovery, Magisk checks the buttons and decides whether you are really trying to boot the recovery. If Magisk decides that you are not trying to boot the recovery, then Magisk chains to the boot image while somehow keeping control.

I do not believe that there is ever a reason for you to unpack or decompress anything. An image file in one of your .tar files may be compressed or not. Odin successfully flashes compressed images. It also can flash an uncompressed image. If the Magisk app finds a compressed image and produces an uncompressed, patched, image, then just leave it as it is. The extensions on the file name may be important to clue in the next stage whether the file is compressed, but it works whether the file in the AP.tar is "boot.img" or "boot.img.lz4".

Don't decompress anything.

All I got out of reading that github issue was that you might have to force close the Magisk app and then run it again. Is that what it was saying? If so, it's simple enough that you might as well try it.

It could be that all of the "traces" that Momo cleverly detects are artifacts of the filesystem that exist separately from Magisk actually running. It may still be that you have installed Magisk, but you have not yet successfully booted Magisk.

You are the only one who could possibly know what you have done. If your most recent Odin run was flashing an AP.tar that was patched to install Magisk in recovery, and you *did* go directly from flashing with Odin to booting the recovery, then you have Magisk installed in recovery and you just have to get it to boot. The few times I have done it it was very frustrating, but after a dozen attempts I finally got it to boot Android. There are other posts (maybe in other threads) giving clues like which signal (Samsung logo, device vibrating,...) is your signal to let go of the buttons. As long as you start with the buttons that are used to boot recovery, if you end up in Android, then you have succeeded.

Try booting to recovery and letting go of the buttons before it gets to recovery. A dozen times. Maybe two dozen. Then go look for a post describing some magic way of doing it effortlessly, like having a USB cable attached to the device, using "adb" to boot to recovery, or booting to Safe Mode and finding that that gives you an option to boot to recovery.