[Galaxy Note 4 Android Development (Snapdragon)] AnonVendetta:
Smart card manager is a system app, it won't show up as a regular app. It's not in the app drawer, and not mentioned in Settings either, unless you unhide system apps. There are no obvious settings for it that have a GUI, unless you trigger them with Activity Launcher, etc. While I was working on the ROM, I noticed that it would randomly crash for seemingly no reason, even though everything else was fine. After some investigation (months), I decided that the app has no apparent use to the average user, and deleted it. Crashes are gone and everything works the same as before. I know what a smart card is, and I'm sure that a very tiny % of users may use them, but most don't even know what they are.

I have repeatedly tested MicroG over the months and found that it is NOT reliable for everyday use with this ROM. Sometimes it would crash randomly, some other apps wouldn't work with it, and just generally other funky behavior that magically ceased after MicroG was removed and replaced with GApps. I used to love it but had to move on, I'm back on regular GApps. I recommend that users not use MicroG with this ROM, but I won't try to stop them. If I can get the new build exactly as I want it, it will be somewhat debloated BUT the core GApps system apps will still be present. I believe that it's too much of a headache to maintain GApps/non-GApps versions. And I will leave the signature spoofing patch as-is, which means that you'll only have to manually debloat GApps and install MicroG. Not difficult, just use the gapps-remove.txt from an OpenGApps nano zip as a reference for what to delete.

There are 2 Google system apps that you shouldn't mess with, they are Android System WebView and Google Package Installer. The latter's function is obvious, whereas Webview provides core functionality that many, many apps rely on. Just don't touch them, period.

I've found that stock N4 batteries tend to degrade very fast (less than 6 months), I've never gotten decent life with them. So I'm not surprised.

If you're willing to do a bit of hunting, go look for either a Zerolemon 10000mah or a TQTHL 11800mah. I've searched high and low for either in the past few months, they seem to be out of stock everywhere I've checked. There are also other extended batteries for our phone that might be worth looking into (less capacity than the ZL/TQTHL, but still much more mah than stock). And you may have better luck finding online storefronts that still sell them. And no matter which extended battery you buy, they will make the phone substantially fatter and heavier, negating its' slim profile, if you care about that. I never have.

The Marshmallow security thing has never bothered me. Yes, it's old, but it works. I personally don't feel like my device is any more at risk than it would otherwise be, but I'm a responsible user and am careful about what I run on my devices. As long as you trust the apps you use and they come from reputable sources, I would say that any worries you have are inconsequential at worst.

However, there are some Pie ROMs for our device, and a new version of Flashpoint kernel was released for Pie too. The last time I used both together, the overall experience was fine. No obvious crashes/issues, except when testing EdXposed. Magisk worked fine too. Might be worth a try. Back up the stock ROM in TWRP, then flash Pie and FP kernel together, run it for a while. If you don't like what you see, you have a reliable backup to return to.

The Note 4 as a device is getting quite old, having been released over 5 years ago. Its' hardware is too old to run anything new-ish with good performance. It's like an elderly person trying to compete in a running marathon with people in their 20s. And I do occasionally experience severe lagging, despite heavy debloating and only having installed what I actually use. Over time I've come to the realization that the N4 just can't cut it. It does what I need it to do, but oftentimes drags its' heels in defiance.

I've had so much fun with this old thing, ROM flashing and whatnot. I've owned at least 4 Note 4s over the past 5 years, including 2 right now, one that was stolen, and another that died in a battery fire. But eventually, we have to move on. I'm not saying that I'm doing so right now, or putting a time line on when I'll buy a new phone and retire this one. However, after I replace it, I will likely keep it as a WiFi phone and run it until it just won't turn on anymore.

As such, I will work on it when I can, but I make no gaurantees in regards to how long I'll continue. Once I buy a new phone, it will probably become the focus of my development efforts. I already own a Tab S7+ that I would like to develop for. Believe me, there is a night and day performance difference between that tab and the N4.

Out of all the phones I've owned over the years, I like the N4 the most, and I've used it the longest by far. One day I'll have to say goodbye, and I'm not looking forward to it. I think it will be quite awhile longer before I find a phone that impresses so much that it becomes my new fave. My tab is super nice and has a huge ultra HD screen, phenomenal performance, but it's not a phone, so no native calling/messaging.