In your last screenshot, the Computer Authorizations are the computers that are allowed to play content such as those purchased for Apple Music. This does not include any iPhone, iPad, or Watch and is only for computers. Any previous computer you had is counted here if you did not specifically Deauthorize it, although the Support Article below does say you can Authorize a single computer twice, but I have never done that. You do not see a list of the Computer Authorizations, so all you can do is Deauthorize a computer that you still have, but no longer need it Authorized to play music (or other content), or Deauthorize All using the button next to it and then Authorize the computers that you want. The details about doing that are found here:
Authorize or deauthorize your computer for Apple Account purchases - Apple Support
The next section is the Manage Devices and these are the iPhones, iPads, Watches, that can download from the App Store. I assume you tapped the button next to it to see the Managed Linked Devices. There is a limit of 10 devices you can have here. You can remove devices that you no longer need. This is not the same as the devices that are logged into your account. As you can see in the screenshot in the Support Article listed below, there is not a direct link to when the device was associated and how many days are remaining before you can remove it. If you have the remove option, you can remove it immediately or wait the days that it shows. It also suggests signing out of the Apple ID on the device if you cannot remove it. I agree that it seems scary that it is listed under Hidden Item, but that refers to the purchases that are made in the App Store and you can unhide them. This is a new change having the setting for your Associated Devices being listed there.
View and remove your devices that are associated with your Apple Account for purchases - Apple Support
About 6 months ago there was an issue where these numbers were incorrect and it would not let you remove the Authorization, but I haven't heard anything lately about that problem. Back then, users were advised to contact Apple directly and they could remove them on their servers and it would be updated on your device. It may have popped up again with Mac OS 15, but again I have not seen that problem since, so if that appears to be the case for you, here is the link to Contact Apple:
Contact Apple for support and service - Apple Support
Your first 2 screenshots appear to be from the Apple server being down. This is always due to a problem on the other end, not on your device. Usually servers will go down just for a short period of time, although may be longer if due to maintenance or heavy demand. I do know if you attempt to sign into the Device Management where it says Work or School Account, you will get an error and it will fail if one does not exist.