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1. https://wiki.termux.com/wiki/Main_Page#:~:text=do%20not%20in...
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1. https://wiki.termux.com/wiki/Main_Page#:~:text=do%20not%20in...
[1] https://www.xda-developers.com/termux-terminal-linux-google-...
That sounds fine/good for like 98% of extensions. But the other 2%... extensions like GreaseMonkey/VioletMonkey/TamperMonkey, or one could imagine something like IFTTT or PushBullet, where the extension might perhaps want some intrinsic extensibility to itself: those are all now verboten. There's not really any discussion or push/pull on the new security regimes. Computers just get more and more clamped down.
I'm interested to see how Termux goes forward. In the past they seemed to have some "in-APK packaging" notions for how to deal with Android 10+. I haven't stumbled upon a good description of what this is or how it would work, and I'm not really sure whether these ideas are still active or whether F-Droid and using ever aging SDKs is the way forward.
There are also other APIs that are absolutely verboten by Google Play but will work fine if the app is installed through alternative app stores.
More recent versions will just kill the application if they get used, and Termux folks refuse to accept that they have to go through JNI for specific OS features, so they won't be around for much longer, other than on rooted devices.
Or they might eventually accept how things are done on Android.
The official APIs are Java based, ISO C and ISO C++ standard libraries, and the NDK libraries that ship on device.
Series 30, Series 60, brew, J2ME, Psion OS, Pocket PC,....
They were never general purpose computers.
Personally I think it's hard to justify phones as something different than general purpose computers. A device that can load fairly arbitrary apps is already almost by definition a general purpose computers, it's just a matter of what has been built and/or what is allowed to be shipped, and what system resources are available (few, in many of your examples, often owing to it being the aughts). Now that the system resources are clearly no longer a differentiator, it's almost all just corporate-politics & the war-against-general-purpose-computing vested-interests enforcing the distinction.
Not everything with a CPU needs to run yet another UNIX clone.
There are plenty of computers and maker boards for that purpose.
Given that the way you say "things are done on Android" is that tools like termux don't exist, you're effectively saying they should just give up and kill the project. I understand that this is consistent with your view of the OS, but can you understand why nobody involved is interested?