Hello everyone!!! I would like to share my recent experience. Yesterday I installed three firmwares on my phone and everything with the October security patch from Google. So, on these firmware, more than one unsigned apk is not installed at all! Installed LSPosed and CorePatch 3.7 and all to no avail. Before that, there was a firmware with some kind of summer security patch and everything worked fine there. So far, there is only one way out, except for CorePatch, install LuckyPatcher and in its Xposed settings check the "disable signature verification in package manager" parameters and apply! Then all the apk will be installed!
In general, I conferred with knowledgeable people and they suggested that the Chinese, in the latest Chinese miui firmware, had built some kind of security patch into the standard application installer and therefore this installer does not skip unsigned or modified apk files. There are two ways out, use a third-party file installer or use localized firmware based on Chinese from the MiuiPro crew, this patch is apparently cut out in it and only in it, through the standard miui installer, such apk files are installed. That's it!