Documentation needed for Android Secure Backup

### Steps to reproduce


MY STEPS TO SHOW WHAT IS NOT DOCUMENTED ABOUT ANDROID SECURE BACKUP:

Make: Samsung
Model: SM-T580 (Galaxy Tab A)
OS: Android 8.1.0
Element Version: 1.5.22 [40105221] (G-bdd431d2)
Matrix SDK Version: 1.5.22 (bdd431d2)
olm version: 3.2.12

Android - Samsung Tablet - Element App - Secure backup

Old / Original Account: CatMan7Life

NOTE - What you need to already have in advance in order to create a "Secure backup":

What this actually means is that you have to first Have performed a 'Key with passphrase' backup before hand

You will then need to select/choose a key backup file already on your device as a part of creating a "Secure backup"

* Personal Recommendation: Create a new/current Key with passphrase *BEFORE* creating a "Secure backup"
- do NOT use a pre-existing older key with passphrase file

OPTIONS CHOSEN:

Settings
Security & Privacy

Heading: Secure Backup
Tap on "Set up Secure Backup"
Info displayed beneath:

"Safeguard against losing access to encrypted messages
& data by backing up encryption keys on your server."

Small grey window/box appears at bottom of screen

************************************

Secure backup

Safeguard against losing access to encrypted messages
& data by backing up encryption keys on your server.

Setup >

! This will replace your current Key or Phrase.

Above message is in Red color

************************************

Tap on "Setup"

A different small grey window/box appears at bottom of screen:

************************************

Encryption upgrade available

Enter your Key Backup recovery key to continue

*** What this actually means is that you have to first Have performed a 'Key with passphrase' backup before hand
You will then need to select/choose a key backup file already on your device as a part of creating a "Secure backup"

Small green rectangular field appears underneath with
The text in the middle:

"Key Backup recovery key"

In the middle of the screen is a gigantic list of session data for encrypted messages (E2EE) that i can scroll through with a green border on the sides
You can tap the middle of this field and type or edit the code
There is a very small grey colored scroll bar on the right-hand side of the input field

Underneath the green rectangular input field are 2 buttons:

USE FILE

CONTINUE

You can optionally click on "USE FILE" which will load
up a file manager requester for you to select a file from

I choose an already exported file from android element:

"Element-megolm-export-@cat7life_matrix.org....

NOTE:

I selected a little bit of the text in the field
I then selected 'All' from the window and then choose copy

The entire window list of all the Megolm encryption/decryption stuff suddenly scrolled all the way to the very bottom of the screen !!!

WHAT I WANT TO BE ABLE TO DO:

I use Element Web under linux using Browser Brave
My situation is that under this element user account, i have a number of rooms that have non-decryptable messages in them on web element using the browser brave

My Samsung TAB however can read all the messages and all the messages are also there (unlike on any of my 3 different linux PCs using element web with browser brave)
I want to be able to have all 3 of my linux PCs be able to

1. Sync ALL the messages i have in my rooms
2. Be able to decrypt all the messages in the rooms - presumably by somehow the decryption keys from my android tablet

I ended up with a situation where my samsung tablet had a requester at the top of the screen saying it needed to communicate with another matrix.org client app (not element) and i was only given the option to use the 'Secure Backup' - but i dont know how to use the android options here
I did post in the official element android room on matrix - i got no responses

Please help documented this and provide at least 1 real example of how to use
Thanks devs :)

### Outcome

#### What did you expect?

I expected a function set to be exactly the same as the official desktop element app/element web

#### What happened instead?
Did not get to use features, as not documented

### Your phone model

SM-T580 (Galaxy Tab A)

### Operating system version

Android 8.1.0

### Application version and app store

Element Version: 1.5.22 [40105221] (G-bdd431d2), Element Version: 1.5.22 [40105221] (G-bdd431d2), olm version: 3.2.12

### Homeserver

_No response_

### Will you send logs?

No

### Are you willing to provide a PR?

No