I have a C7 at home and did the update to 2.4.0.150 well after installing PM. I have a second location I am setting up using a C5, and I was prompted to update -- so I did.
What I found was that no documentation, video or file seems to be able explain how to import PM into this new UI major revision. In fact, I could not even find developer mode, and Restore from Settings just couldn't cope with bad JSON files (it says).
I got around it by going Advanced, rolling back to the previous 2.3.x.x version and loading PM and my drivers. I am about to do the update to 2.4.0.150 again and expect all will survive just fine, as it did at my home.
Something dramatic has changed that seems to have voided the explanatory materials online to install and use PM. This is too bad because with so many Tuya and other products, it is the easiest way to get on and keep on top of the hardware you are installing.
Hopefully this will get resolved soon -- but at least you know workaround in the meantime.
Sounds like you are talking about the "Show advanced/developer options" toggle on the Settings page. On new/fully reset hubs that defaults to off and must be toggled on to enable access to those capabilities.
What I found on the reinstall was that 2.4.0.150 completely obliterated the Platform Manager and thus the user drivers. A restore of the image taken before the change failed to deliver the goods too.
I did follow your advice and found that the Bundles section reappeared (as did drivers) and I was able to import a .zip bundle for the PM. I will continue testing, but this modest little item of the switch that you showed is the real key to a clean/new-ish HE coming alive.
I assume you mean "HPM" or "Hubitat Package Manager" (I am not familiar with anything called "PM" or "platform manager"). This is a custom app. Documentation for how to use and install these is not and cannot be provided by Hubitat other than the general instructions applicable to all custom code, which you will indeed find in the user interface documentation, among other places:
This may not be apparent if you don't know what to search for, so hopefully this helps. Each link there is also a link to another page with more information about that UI page.
If you found HPM documentation that is outdated or lacking, a kind request to the developer may also be helpful. These are all recent changes to the UI, made in the last major release. As such, lots of documentation, especially from third parties, may still be catching up; and lots of posts you'll find in the community that are older than a few weeks may find things in a slightly different spot.
This should not have happened unless you experienced data corruption, did a soft reset (without a restore), or had some other odd problem. Uninstalling HPM will also not affect any code it helped you install -- it doesn't do anything you couldn't have done yourself, just makes some of it easier. And an app or driver in use (by an installed app or device) cannot be removed, neither by you nor by HPM (or any other means).
Those are two possibilities as to how this could have happened, and a restore from a known-good time should have helped, so it's not clear what went wrong in your case. But glad you're up again in any case!
Prior to updating to 2.4.0.150, I had saved the backup. The installed user app was working fine, and I had added user drivers using it.
Once the update was done, then the app and drivers were absent. A restore failed to put them back.
I did no resets -- that only being a possibility of the process doing the update inducing such a reset.
I agree that it should not be impacted, but it was and I have gotten past that. As you said, maybe something got corrupted and unbeknownst to me, a reset occurred. Why the restore failed, I cannot say.
So time to move ahead to try and get this hub "registered". This appears to be more complicated that I might have hoped with the methods using this latest release being hard to ferret out.
