I’ve permitted ‘Install Unknown Apps’ in some cases in the past without any issue.
However when trying to do so now, I’m unable to change the settings to permit ‘Allow from this source’.
Has some default setting with /e/OS change lately?
Using:
Teracube 2e
/e/OS v2.9-s emerald (current version)
Regain your privacy! Adopt /e/OS the deGoogled mobile OS and online services
Files app has changed such that it must be given “Special app access” in order to deliver the file for installation.
Search Settings > Special app access > Install unknown apps …
Thus if you find on device your .apk with Files, then Files needs to have toggle on “Allow from this source”.
Thanks for the info.
Needed to allow Magisk this access in order to ‘hide’ the app.
Could easily access the Install Unknown Apps in settings, however the slicer to permit access appears to be locked. In other words the slider will not change to green.
I wrote by way of example about Files app … while my expectation is that Package installer will be responsible for the install, I find, on my phone that Files app has the permission Install unknown apps … perhaps this is a requirement before Allow from this source.
I located the problem … it was me. 
Was doing some work and left the phone in developer mode. Took it out of developer mode and all was working as I would have expected it to.