Nvm, I think I have it figured out. I started cross referencing everything between by laptop an desktop and was able to kind of figure it out.
I never used any repos version of dotnet, only the version that Rider installed, so Rider was managing all of the versioning. I removed all the repo versions of dotnet, reinstalled Rider, and was able to install the 8.0 and 9.0 SDKs through rider. My target was 6.0 but I just right clicked the solution > Properties > chose 9.0 as the target and up and running.
Thanks all for your input! It helped my look outside the box of what I was already trying.
P. S. Specifically after uninstalling all dotnet versions and reinstalling rider, in order to download them I went to create a new project, chose the version of dotnet I wanted, and Rider would give me a prompt to download the missing version since it did not detect it anywhere. They were downloaded and installed at /home/your-user/.dontnet/sdk. Jetbrains didnt even give me an option to select dotnet 6 so I assume it must be deprecated since I last installed it. Right clicked the solution in the file view in the left hand pane, clicker properties, and chose dotnet 8 or 9 as the target framework