[Nokia Lumia 1020] Neoloko:
Regarding #1 ---- I did flash the file Backup.zip as a custom ROM using WPinternals. was that wrong? Also, does flashing the file back again mean that I will lose all the installed updates and apps?

I think it'd be much easier if I can get the Lumia Camera app and install it directly (not via the Microsoft Store)

Search in google how to do it, ,because in this way I have not done it, you will need set the phone in the developer mode and using the appx file from there:

https://www.appx4fun.com/s.php?s=lumia

Regarding #2 ---- Actually I thought reverting back to the original phone identity was the only way to get the Lumia Camera app as it's meant for Lumia 1020 and similar Pureview phones.

this is other option, go back to original OS and add this app in your account store to get your nokia camera, or use this --> App Data Manage tool (beta) --> search on google this app ----> how install and used it in your original Os, this app let you make a complete backup of all i mean all apps (copy this backup files from your phone to your pc ) and you can try restore this when update to win10, but i am not 100% completely sure thats work in last win 10, but this one way to try get the orginal appx file from nokia

Regarding #3 ---- I never installed Lumia Camera on my phone coz Nokia Camera app was much better and I do not have it in the store library.

Can you direct me to where I can get the installation package file for Nokia Camera or Lumia Camera app?

https://www.appx4fun.com/s.php?s=lumia

Do you think MS just stopped support for these apps in ver. 10.0.15254.527?

i have all lumia camera staff working on me lumia 1020, even more me lumia is an rm-877 and i am flash on it the rom to rm-875 with win10 (build 1709-10.0.15254.527 ) (of course the firmware is lumia denim version 3051.50009.1451.1004 ) and it work

Further Questions (Sorry):

1- I did not encounter any instance of the "Equalizer" app at all!!! What was the problem installing this app in the first place? And should that problem occur by installing other multimedia apps related to playing audio/music (like Groove Music)??

the equalizer is on extras menu, the issue is , in the first version this app is called audio and it include the equalizer and other options like dollby ,standart volume level and other options which only work when use audio cable conection, , and the new o last version updated this features are deleted and only you will see the pure Equalizer, no problem with other audio apps

2- Glance Screen does not work and I can not find any reference to it in the settings! I remember reading that it's working in this custom ROM!

3- The settings does not have any configuration options for the touch screen sensitivity and it's really annoying when it's ultra sensitive. Any suggestions?

to setup Glance Screen and touch screen go to settings-->extra&info you will see it there.

the questions about from 2 to 3 can be solved using Interoptools search it on google

or use :

These are WM10 compatible OEM apps for Microsoft/Nokia Lumia devices: What apps are included?

Advanced Info (advancedinfo.appx)

Equalizer (audio.appx)

Color Profile (displaysettings.appx)

Glance Screen (glancescreen.appx)

Lumia motion data (motiondatasense.appx)

Network services (networkplus.appx)

Touch (touchsettings.appx)

Devices Hub (devicehubspiderman.appx)

https://onedrive.live.com/?authkey=%21ABRihRRvkwDlNKc&id=82E12CC32F8AF242%2186580&cid=82E12CC32F8AF242

4- Does the "Brightness Bar" mentioned by some users provide lower screen brightness level than the low option available with this ROM? And how can I get it?

brightness slider is enabled use Interoptools search in youtube the video

"How to Interop Unlock windows phone 10 and enable Brightness slider without using PC"