Tahoe Upgrade made my computer impossible to use.

I have encountered some bugs with Tahoe, as is to be expected. But overall it works well enough. In particular, I do not have the problems you describe. Here are some standard troubleshooting things to consider.

Are you running a 2019 (intel chip) MacBook Pro? I did not find the performance of Tahoe to be very great on that machine, although it was certainly usable.

Have a look at the application Activity Monitor and see which, if any, processes are using lots of CPU.

Does this occur for a different user, e.g., Guest ? 

Change Users & Groups settings on Mac - Apple Support

Does this occur after starting up in Safe Mode? 

Consider the possibility of a third party software conflict.  EtreCheck can be used to investigate what is installed.  Give it full disk access. You can post the report here. Someone might spot something.

Using EtreCheck to Troubleshoot Potential Mac Issues

GnosticLibrary wrote:

I did the upgrade and finder is accesible now and screenshots are workign again. Still 3rd party devices like my mouse are not working.

I am sooooo dissapointed on apple. How could you lauch such a non-reliable upgrade like this?

To be proactive you can file a bug report / submit your Apple Feedback here: Product Feedback - Apple

The current stable release of Tahoe including bug fixes, security updates is macOS 26.0.1

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support