In my experience, the newer the Windows server OS is, the faster and easier it is to setup and support.  And the sites always run faster.  Windows tends to focus on that as it too gets upgraded & updated.  

Upgrades can be complex - especially when a lot of 3rd party modules are involved and not maintained well. That said, what version .NET Framework are you running? Is it 4.7.2+?

Ok, strange thing. The moment I installed the upgrade for the Feedback module things went south very rapidly.
Errors started popping up here and there and paging controls for the Host Settings page failed. Everything was expanded and the "collapse" arrows stopped working.
How did one Feedback module upgrade break my DNN installation?

p.s. I did not backup my installation before installing a module... never thought an official module could break my installation

Did the whole process over again, backing up the working DNN 8 installation so I can reiterate Feedback module installs until I find the version that works and doesn't break my installation.

After restoring the DNN 8 version that worked on my Windows 2012 server I get this error on the windows 2022 server

Could not load file or assembly 'ChilkatDotNet2' or one of its dependencies. An attempt was made to load a program with an incorrect format.
Any idea what this means and why I didn't have the same error on the other platform?

The files are the same and the Database is the restored backup and therefore identical. It works on the other machine, It throws an error on this one. Why?

I have solved this error previously by simply removing the ChilkatDotNet2.dll file from the "bin" directory, but given nothing really worked after I did that I guess I'll try to do something different this time around.

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.8.4718.0

Looked around in the forum and someone suggested to activate 32bit applications in the App Pool... seems to work :)

Eureka! It's up and running! And the paging works, and so do postbacks!
The host settings page works and so does the Admin Pages page.

Now I only have to find a Feedback module version that doesn't break my DNN installation.

 

Like David said, some upgrades are complex. First and foremost, I would recommend starting over from a known working state. Then I would remove all unused extensions. After that I would upgrade all extensions to the lasted version supported by your working DNN version.
SolPart was removed at some point in DNN, so you will probably need to update your them and then start with DNN upgrades. Looking at the errors above, there are many completely unrelated errors, so you may have several issues to handle.

Yes, about that, I tried uninstalling some older extensions I'm not using but I get an error and they keep appearing in my installed extensions list.
The error I get is this:
Error: Not currently available DotNetNuke.Services.Exceptions.ModuleLoadException: Version string portion was too short or too long. ---> System.ArgumentException: Version string portion was too short or too long. at System.Version.VersionResult.SetFailure(ParseFailureKind failure, String argument) at System.Version.TryParseVersion(String version, VersionResult& result) at System.Version.Parse(String input) at System.Version..ctor(String version) at DotNetNuke.Services.Installer.Installers.FileInstaller.ReadManifestItem(XPathNavigator nav, Boolean checkFileExists) at DotNetNuke.Services.Installer.Installers.FileInstaller.ReadManifest(XPathNavigator manifestNav) at DotNetNuke.Services.Installer.Installers.InstallerFactory.GetInstaller(XPathNavigator manifestNav, PackageInfo package) at DotNetNuke.Services.Installer.Installers.PackageInstaller.ReadComponents(XPathNavigator manifestNav) at DotNetNuke.Services.Installer.Installers.PackageInstaller..ctor(PackageInfo package) at DotNetNuke.Services.Installer.Installer..ctor(PackageInfo package, String physicalSitePath) at DotNetNuke.Modules.Admin.Extensions.UnInstall.UnInstallPackage() at DotNetNuke.Modules.Admin.Extensions.UnInstall.cmdUninstall_Click(Object sender, EventArgs e) --- End of inner exception stack trace ---

Some modules do not uninstall correctly, although they should, old systems are difficult to maintain just because of the way things change of the years. It's often not even the developers fault. It can be possible to uninstall manually by deleting files and updating the database, if you know what the modules contains. The version error would make me to start looking at the manifest (if it's in the module folder) and the SQL installation files. However, keep in mind that some modules have dependencies on other modules, these can cause other problems.

I'm sorry to say that without a good backup you're on the edge of a cliff. Maybe you should try and get the client to rebuild in DNN9.

Good Luck!!