Creating assetbundles in 2021 for Unity 2019 (backwards compatibility issue)?

Hi, I have created a VR game that uses Unity 2019 runtime and I am unable to upgrade the project to 2020 at this time due to Unity dropping support for VR after 2019.

But many of my users are now creating assets using Unity 2020 and 2021 editor.

I tried creating a basic asset using Unity 2021 and opening it in Unity 2019 but received error:
Failed to load 'archive:/CAB-4905ecd673d9920e3435ef309b05a0f5/CAB-4905ecd673d9920e3435ef309b05a0f5'. File may be corrupted or was serialized with a newer version of Unity.

-or-

The AssetBundle 'folder\vr assets\test scene.scene' can't be loaded because it was not built with the right version or build target.

Does this mean there is no way to create backwards compatible assetbundles in newer editors so I can use in Unity 2019 (LTS)?

Maybe there are option I could set or some things I need to consider in order to create backwards compatible assetbundles?

Please help me understand why assetbundles from 2020 do not work in 2019? I thought in Unity the assetbund version recently changed to 2.0 or something. but is there now a 3.0 version in 2020?

Thank you

 

I think the word on this is that newer unity runtimes have backwards compatability for bundles built by previous editor versions, but old runtimes are not gauranteed to be able to load bundles generated by a newer editor.