I have patched in inputstream.adaptive on my RPi3B+.
WARNING: ITS NOT TRIVIAL AND QUITE TECHNICAL. (Most of the work is from the command line - no gui.)
Here’s how to do it for a Raspberry Pi.
1) First you need the plugin for your architecture.
To do this I built a clean Raspberry Pi OS Lite system on a spare microSD card. After configuring the network, language and keyboard, I installed kodi-inputstream-adaptive using apt. There are 2 subdirectories for it that you need to copy. One is in /usr/share/kodi/addons and the other is in /usr/lib/arm-linux-gnueabihf/kodi/addons. Zip both of the inputstream.adaptive subdirectories from these locations.
2) Transfer these 2 zip files over to your Batocera system.
Run ‘mount -o remount,rw /’ to make the root partition writable
Unzip the file from /usr/share into /usr/share/kodi/addons
Unzip the file from /usr/lib into /usr/lib/kodi/addons
Run ‘batocera-save-overlay’ to build an overlay file and make the changes persistent across reboots.
If you do not understand how to accomplish the steps I have outlined here, then this is too technical for you. Wait for the developers to add the plugin into the build.
Here is a package of the required files for the RPi3. It may work on the RPi2 but definitely won’t work on any other architecture.
https://wetransfer.com/downloads/6c67ba301477a3d33951c1b5956c866120200627212158/617a4ff3db3baff3e3ab95733cdb6a7c20200627212240/29018d
The link expires in 7 days.
Good Luck!