[Samsung Galaxy Note 8 Questions and Answers] jooniloh:
I just got everything working on my Tab S8 Ultra and thought I'd share my method.

The problem here seems to be that the pull/install method does not work for split APKs. It also seems that the Aurora Store struggles with installing split APKs as well. With the Dual version of Aurora Store, I could install the Wikipedia app as a Dual app, but both the base user and Dual versions of Aurora Store could not install Activity Launcher or TikTok (gave an error every time, even when the app in question was uninstalled from all accounts). Furthermore, unlike @chicken10dys, I could not get the Play Store running at all after cloning it via the pull/install method.

Some setup to make life easier now and later:

Get Applications Info from the Play Store to easily find package names without having to read through the output from pm list packages.

Optionally set up LADB and wireless debugging to make your life easier and do this all from your device without having a computer on hand.

Note that if using LADB, any commands that start with adb shell should omit adb shell entirely but all other adb commands should include the adb.

Install Activity Launcher from the Play Store and use the pull/install method to install a copy on user 95 (this works for some reason, even though Aurora Store couldn't install it.

Launch the Dual version of Activity Launcher and find the Dual version of the Settings app near the bottom of its list.

Under Settings, find Settings again (or specifically, com.android.settings.homepage.SettingsHomepageActivity.

Do not launch this directly, as for some reason, that will still open your base account's Settings app. Instead, create a shortcut to it via the 3 dot menu on the right. The newly created homescreen shortcut (again for reasons unknown) will correctly launch the Dual version of Settings.

You can use this Settings panel to do things such as adjust the "Full screen apps" settings for Dual apps (to hide/show camera notches) and to toggle other app-specific settings only available from the Settings Panel (Auto rotate apps for tablets is another one).

You can use this same method of launching the account-specific version of Settings via Activity Launcher to configure the same settings for Secure Folder and Work Profile apps, by installing a copy of Activity Launcher in those accounts as well.

Here's what I ended up doing:

First, I needed a split APK installer. My first thought was the APKMirror installer, but after installing it to user 95 via ADB, it failed to open for whatever reason. So next I tried installing SAI from the Play Store, and then pulling/installing it via ADB to user 95. This worked. I now have a Dual version of SAI installed.

Next I granted SAI permissions so it could read the file system. You can do that either via (L)ADB, or using Permissions Manager as mentioned by someone above. I also took this opportunity to allow SAI to install apps.

After that, I downloaded the latest .apkm for TikTok from APKMirror (the MIDDLE option here: https://www.apkmirror.com/apk/tikto.../tik-tok-including-musical-ly-23-4-4-release/). I then used My Files to move the .apkm file from the downloads directory of the base user to the downloads directory of the Dual user.

Then I launched SAI and selected the .apkm file from the filesystem and waited a bit. As TikTok was already installed on my base user, it did show "Update" rather than "Install", but it continued fine after selecting that, and in the end, I was left with a copy of TikTok that didn't crash upon launching!

If you've done my recommended steps above, a couple additional things you can do:

Save some of the more frequently used ADB commands in LADB so that you can quickly use them again in the future (makes pulling locations, granting permissions, etc. a lot faster).

Use the Dual settings app to adjust whatever settings you'd for your newly installed Dual app(s). Personally, I always set my apps to use the full screen, regardless of any notches/cutouts, and to force resize to the full aspect ratio in any orientation.

Finally, as a little bonus, I present to you 4 instances of TikTok running simultaneously on my Tab S8 Ultra via Dual Messenger, Work Profiles (Island), and Secure Folder for absolutely no good reason whatsoever. 😂