You said Tincore is becoming harder to set up recently, has there any "regressions" with Tincore for the last few versions?
Supposedly there was a "beta" channel for Tincore in Play Store. But even after signing up for it, there were no versions past the latest one.
Again, I've no idea why Tincore can generate stuck touches when waking up even after minimizing/disabling it. (Technically if I minimize/disable the keymapper, no more touches should be generated)
Lastly, is it possible and practical to inject SELinux policies needed by Tincore for necessary operations like detecting devices, so I can use Tincore while keeping SELinux Enforcing? If the policies are heavily device-specific, a guide for how to manually inject them would be also helpful.
None that I could tell. It's just that the settings wouldn't stick, or the profile wouldn't load with the game. But that may have been due to the way Snail devices handle physical controls. I haven't used it on any other than a Snail device.
I agree with Skelton's idea. If possible, try a less modified ROM.
Sorry, but I don't use Snail devices right now... (I did in the OP mentioned that I'm now using Asus Zenfone 2 with an external bluetooth controller). Back then with Snail devices, up to W3D, everything works well even after I heavily modded the system with Xposed.
Maybe it's possible that AOKP has some underlying incompatibility with Tincore, as I originally did not observe the issue (maybe I did not pay attention) when I was running Resurrection Remix (which I eventually ditched due to it often reboots itself at night, which is not the case for AOKP). Maybe I'll try something different, but the main reason I chose AOKP was because of the OMS and the fact that it's still being built.
Guess I'll check out the most recent AOKP build for my device and try flashing it and do some further tests to find out if the problem is indeed with the ROM not Tincore but that's not likely to be certain.
I use tincore on mu shield tablet with nougat with no issues. I use SELinux permissive. It's not a problem to have SELinux permissive, there are no potential risks. There is more risk just being rooted that with SELinux policies. So I would put SELinux permissive and should work fine, unless it has issues with your device or gamepad for some reason.
The more AOSP the rom the better, and I see you are using AOKP which is heavily modified from standard AOSP, so maybe that rom is the issue.
I'm no expert on what SELinux controls and what SELinux polices can pose risks. For a while there used to be devices with custom kernels built with SELinux set permissive by default (around Lollipop, I think), but recently people started going against that idea. Safety Net might be a factor, but it seems Magisk Hide is able to keep SELinux settings from tripping it.
An example of working around the SELinux requirement would be Viper4Android, which used to require SELinux permissive, but not anymore, as by community demand, they seem to have created scripts that perform all the policy injections so the app can function properly with SELinux stay enforcing.
PS, there has been a script for Magisk
that helps users setting SELinux permissive, but the developer stated that such should only be a last resort and recommended that users to "contact the app developer and try to work with them to isolate the necessary SELinux Permissions and have them injected into the SELinux Policy at startup".
He also stated that "Putting your device into Permissive Mode will essentially disable all of the operating system level security built into Android and allow any app in any context to do whatever it wants". I think he might be referring to apps with "really" malicious intents.