Hi,
I'm coming back since I've found a workaround for Galaxy Wearable to work again.
So here is what I have done (for Samsung device with custom ROM only) :
If it's not already done, install the "MagiskHide Props Config" module from Magisk and then reboot.
Open a terminal emulator and run "su" then "props", when the module is loaded, type "1" to edit fingerprint, choose Google, then Pixel 3 (even if you're not on Android 9). For all of the manipulations when the module asks you to reboot, don't reboot.
After that, go back to the main menu and choose "Improved hiding" and enable it.
Then, go back to the main menu again and choose "Add/Edit custom props". Now we need to change everything that is related to Samsung.
Do theses steps for every prop we need to edit :
1. Type "n" to add a custom prop
2. Now we need to say which prop we need to edit : "ro.product.brand", "ro.product.device", "ro.product.manufacturer", "ro.product.model", "ro.product.name" and "ro.vendor.product.manufacturer" (Type only one of them and without the " ")
3. If the value already exists it will show you what is the actual value of the prop, and if it doesn't exist, double check that you didn't make any mistake when typing it and if not, skip it.
4. Then type respectively : "google", "crosshatch", "google", "Pixel 3", "crosshatch" and "google" (without " ")
5. The module will asks you for when do you want this to be applied ? Just keep "default" and validate with "y"
6. When you have done this for the 6 props, you should have something like the screenshots.
Now you can reboot your phone, delete all the data of the Galaxy Wearable app and it should open ! And also don't forget to hide it with Magisk Hide before clearing data.
What we have done here is to change all of the values of a Samsung related phone to a non Samsung phone, and I think that the app is checking a specific thing (like a TouchWiz related thing), and if it can't find it, the phone is unofficial and the app doesn't want to run. But with the other brands they can't do that so the app is running without problem.
Last thing, if doesn't work even with that, go to Settings, About phone and check if it's now shown as a Pixel 3, if not, there might be an issue somewhere else. Make sure that your ROM passes SafetyNet. Or if you want, you can open a build prop editor, search for "samsung", "zeroflte" (Galaxy S6 specific), etc... and see if there is a prop that I/you missed and change it to "google", "crosshatch", etc...
So let me know if it has worked for you : Working on the Note 3, Galaxy S7 Edge
PS : Sorry for my English if I have made mistakes.