Mac M3 sluggish

I would suggest to do the following,

Hold the power button for 5-10 seconds until you get the Startup Options Appear. From there once you have entered the startup options choose the selected disk you want to boot and restart your device. As Mac's no longer have the manual PRAM/NVRAM to reset this would do it automatically using the chipset built in drivers when using this option. If that still does not work back-up all your data and do a internet recovery download and reinstall your MacOS and be sure to back up your data first before attempting a reinstallation of your Mac OS Operating System.

I would also suggest to make sure you have all current updates that Apple has released for your device to make sure there is not bug or patch updates before reinstalling your Mac OS Operating System

also do Get Info on your boot drive - pay attention to CAPACITY - AVAILABLE - USED

emphasis on AVAILABLE -- i like to keep minimum of 40 percent of a boot volume empty (available) -- more if you are running apps like Photoshop that can use tons of free space for its Scratch Disk

a drive that fills up and turns flaky can be a nightmare to get back on track...

DRIVE HEALTH is also a critical area to monitor -- i recommend DriveDX app for checking that

EtreCheck will report these areas as previously suggested

Install EtreCheck and post the report. It may reveal the problem.

https://etrecheck.com/

Use the Additional Text icon to paste in the report.

Just to add, I run Tahoe 26.2 on my M3 iMac and there's nothing sluggish about it.

You might try starting in Safe Mode and see if it helps:

Start up your Mac in safe mode - Apple Support

Another vote for the etrecheck report.

I run 26.2 on my M3 iMac with 8GB of RAM and it performs flawlessly.