So Unity got my ticket but they decided not to fix the toolchain v2 not showing the package manager, as there are two workarounds: delete and reinstall, or edit the manifest as I said.

"After careful review, we have determined that this issue can be easily worked around. You can either:

1. Remove the old version of the package and then add a newer version using the Package Manager, or

2. Manually edit the manifest.json file in your project, as you’ve already pointed out, updating the version number for the package.

Due to the availability of these simple workarounds, we have decided not to prioritize fixing this issue at the moment."

So don't wait for a fix and follow one of the workarounds. But I hope there are not other packages with the same issue, because I'll never know when I need to do a fresh install instead of a mere upgrade check!

It turns out that while the issue itself is fixed when upgrading to Toolchain v2.0.4, there is a bug in the Package Manager UI that prevents upgrading: the Update button won't appear when selecting the Toolchain package (at least Toolchain Linux x64).

So I had to modify the version manually:

1. Open Packages/manifest.json and set "com.unity.toolchain.linux-x86_64": "2.0.0" instead of “1.0.0”. Ideally you'd set the latest version directly (currently 2.0.4), but if you don’t know it, just set it to 2.0.0 for now.

2. Reopen or refresh the project. packages-lock.json should auto-update to match the new version, including sysroot dependencies. With toolchain 2.0.4, sysroot 2.0.5 and sysroot.linux-x86_64 2.0.4, the issue should be fixed.

3. If the errors persist, try a small update: open the Package Manager and select the Toolchain package: this time, the Update button will be present, so you can update to latest patch (currently 2.0.4). This time, the issue should be fixed.

I have reported this issue to Unity so they can reopen a ticket for the UI bug specifically.

It happened to me after upgrading a project from Unity 2022.1 to 2022.2. For some reason com.unity.toolchain.linux-x86_64 was stuck to v1.0. I had to remove the package completely to make it work again. If I want to be able to build for IL2CPP, I can just reinstall it and this time, v2.0.4 shows properly.

You can probably also force upgrade by editing the packages-lock.json and set the version to 2.0.x.

Thx SPOBRIEN1999 !
I'm on windows with unity 2022.2.7, i had the same problem when i switch plateform to webgl. I just update 'Toolchain Win Linux x64' package in package manager and it solved the problem !

I'm on Linux running version 2022.2.1f1

I followed these steps from Unity3d docs. This resolved the compiler so that the project at least loads. I'm still having build issues, but I think these may be from another problem. Unfortunately, the URL checker won't let me post the docs.unity3d page, but here are the steps directly from the docs page.

1.
To use the following packages, you need to install the Linux Build Support (IL2CPP) module in your Unity Editor version.

2.
To install a Unity toolchain package:
Go to Window > Package Manager.
Use the search bar to find the package, and click Install in the bottom right corner of the Package Manager window.
Choose the package based on the host platform.
Linux -> com.unity.toolchain.linux-x86_64
macOS -> com.unity.toolchain.macos-x86_64-linux-x86_64
Windows -> com.unity.toolchain.windows.x86_64-linux-x86_64

3.
When you have installed your toolchain package, go to Project Settings > Player > Configuration and set the ScriptingBackend to IL2CPP.

Still present in 2022.2.1f1 under ubuntu 20.04. Is there some possible fix?

Still issue

Still present in 2022.2.0f1

Still present in 2022.2.0b3 and I don't see any package version 2.0.0 in the manager for installation?

Still present in 2022.2.0b2