Question Fix UnityEditor.Experimental.UIElements compile errors in Unity 2019.4

[SOLVED]

I am following the course "Create with Code" and I downloaded the assets to get started. However, I noticed a large number of compile errors. On looking closer, I found the the error to be in UnityEditor.Experimental.UIElements. My first guess was since this tutorial was made in 2018 version, this might've been moved out of Experimental stage. I looked up some documentation and it was indeed the problem. So, I started removing Experimental from all the lines. It worked and errors seemed to disappear one by one. But even after doing all that, the fix seems to be temporary as the old files kick in as soon as I [save] and close Unity. I know I am doing it wrong, so I need help on how to overcome this issue.
I'm using Visual Studio Community 16.7.4 and Visual Studio Tools for Unity 4.7.0. I don't know if it's helpful. But extra info won't hurt ig.

My unity version: 2019.4.10f17

EDIT 2:
As Brathnann said, going to Package Manager (Window > Package Manager), then changing Unity Registry to My Project and finally updating (click on the update to 2.2.2 on the lower right, I missed it at first. I'm dumb) Package Manager UI to 2.2.2 has seemed to solve the issue. Thank you Brathnann.

EDIT:

I've got like 125 of these compiler errors:

Library\PackageCache\com.unity.package-manager-ui@2.0.7\Editor\AssemblyInfo.cs(7,12): error CS0246: The type or namespace name 'UxmlNamespacePrefixAttribute' could not be found (are you missing a using directive or an assembly reference?)

And 16 of these warnings:

Library\PackageCache\com.unity.package-manager-ui@2.0.7\Editor\Sources\UI\Common\Alert.cs(19,28): warning CS0109: The member 'Alert.UxmlFactory' does not hide an accessible member. The new keyword is not required.

Screenshots:

 

Great to provide more information, but you failed to provide a very key piece of info...a copy of the error you are getting.

I would copy and paste an error and if you can, show the code related to the error. That's going to always be pretty helpful when trying to fix compile errors.

 

Damn, I did miss that lol. I'll paste it here, and if possible, edit it out in the original post.
I've got like 125 of these:

Library\PackageCache\com.unity.package-manager-ui@2.0.7\Editor\AssemblyInfo.cs(7,12): error CS0246: The type or namespace name 'UxmlNamespacePrefixAttribute' could not be found (are you missing a using directive or an assembly reference?)

And 16 of these:

Library\PackageCache\com.unity.package-manager-ui@2.0.7\Editor\Sources\UI\Common\Alert.cs(19,28): warning CS0109: The member 'Alert.UxmlFactory' does not hide an accessible member. The new keyword is not required.

Screenshots:

 

Those errors seem to target the package manager ui, which does use UIElements. You may need to update your UIElements and your package manager ui packages.

 

//EDIT:
You were right! Thank you! I updated Package Manager UI to 2.2.2 and it all went away. I haven't tried running it with new code, but apparently it works. If this was reddit, I would've awarded you lol. Thank you!

How do I do that? It's already up to date. And isn't the script (written?) for an older version of package manager? If what I understand is correct, then UI Elements is no longer Experimental as the script is trying to call. I could be wrong, I am a complete beginner.

 

Glad it's fixed!

 

For my Update this package resolve all the errors: