APK Downgrader - Web
Info
This method of downgrading Oculus Quest apps is outdated. Please use Oculus API App Versions (text clickable) instead. Instructions are on the page itself.
Downgrading Beat Saber with this tool will not work. Refer to the info above for the new downgrading method.
APK
Patch
Save as
Guide
Download patches
Pulled from APK Downgrader (click text to download). Red patches may not work on 32 bit brosers as MS Edge, Google Chrome and Opera. It gets Red with 3GB est. RAM usage and more

You can downgrade downgraded apks.
Find the downgrade path to downgrade to your target version:
Source Version (optional) Target Version
App
APK Version
Target Version
Est. RAM Usage

Notes
Tested Devices + Browsers
Tested with Beat Saber 1.15.0 to 1.13.2. Smaller Apps may work on more devices. This data is only by one person each so it might be incorrect. N/A means the browser hasn't been tested/doesn't exist.
Since the Web Version uses lots of RAM atm (read for your patch above) I figured this List would help you a bit. General guideline: Min RAM on light weight OS: 4GB, recommended: 8 GB

Device
MS Edge
Mozilla Firefox
Google Chrome
Opera
Safari
Oculus Quest 1
Y
N
Oculus Broser N
N/A
N/A
Oculus Quest 2
N/A
N/A
Oculus Broser N
N/A
N/A
Android Phone (4 GB RAM)
Y
N
N
N
N/A
Android Phone (8+ GB RAM)
Y
N/A
Y
N
N/A
Windows (8+ GB RAM)
Y
Y
Y
Y
N/A
MacOS 10.13.6+ (8+ GB RAM)
N/A
Y
Y
N/A
N
Doesn't seem to work on IPhones yet cause of Apple putting restrictions on file picking. If you experience elsewise feel free to contact me.
Guide
Instructions, Infos and help with this tool
Tip
If you are on a device which has low RAM then close all Apps/programs except your browser and close your browser or this tab after downgrading.
(About 2GB RAM is getting used when downgrading Beat Saber)
Is this tool piracy?
First of the question: What am I downloading from the Patches section above?

You are downloading a binary difference between the purchased unmodified Beat Saber version you have and the unmodified Beat Saber Version you want to downgrade too.
Stored in those files is how to rearrange the bytes of the APK so it'll be the older version.

So is this piracy?

No. You're not downloading any game code. Those patches will only work (aka give you a downgraded APK) if they get used with a legally purchased version of Beat Saber
Downgrade entirely on your Android Device
Note: This may only work if you use Microsoft Edge which you can download here and install just like the APK Export APK
First download APK Exporter from here (You do this by clicking Download APK on their site).
After that you need to install the APK. For this use any file browser like TotalCommand (which you have to sideload to your quest) or the built in browser of any other device.
Find you downloads folder and install the APK which you downloaded (it should have "APK Export" in it's name).
After installing it open it and click on the app you want to downgrade. Then hit the save icon and wait.

Then come back here and choose your APK. Browse for the APK you just saved (which is in a folder named apk) and download the patch you want to use from the section above.
Then select that one as well.
Hit downgrade and after a bit a downgraded apk should download.

Follow the same steps to install the downgraded APK as you did to install APK Export
Common errors
Errors which may or may not show
Array buffer allocation failed or Browser crashs
This means you don't have enough RAM left. Either it'll not work on your device at all or you just have too much RAM in use.
Browser doesn't do anything after pressing Downgrade
Either your browser doesn't work with This tool or you don't have enough RAM left
I get an out of memory error
This means that you don't have enough RAM left. Try closing all other tabs and Apps. If the problem still occurs (and you have RAM left) Then the patch is too big to be used. You can see estimated RAM usage above.
INSTALL_FAILED_VERSION_DOWNGRADE on Sidequest or ADB
This means you have a version of your app installed which is newer than the one you want to install. Simply uninstall your app before trying to install the downgraded apk (Note: without creating an Game Data Backup in the apps section of Sidequest first you may loose game progress)
Source checksum mismatch - patch is not meant for this APK. [...]
First make sure you haven't tried to mod your game. If this is the case uninstall Beat Saber on your Quest and download it again. Then make a new backup and try again. Otherwise just try backing up the APK again.
Premature end of stream missing 1 byte on Sidequest or ADB
Make sure you haven't checked skip verification as this will skip any checks of your APK, Patch and downgraded APK. This error usually means the downgraded APK is corrupted.
Unknown patch format
Usually this means that your browser doesn't work with the downgrader (so try some different browsers)
Array buffer allocation failed
This error usually occurs on opera and indicates that your device has too little ram available

The Web Version of APK Downgrader wouldn't have been possible without the work of hack64's Web Patcher which is powering most of the code behind downgrading.
Tool by ComputerElite