iMac running slow after macOS Sequoia 15.9 update

After security update, iMac has slowed down. I have an iMac desktop purchased in 2019. Yes, I know it's old but suits my needs. I just updated to Sequoia 15.9 for security and it has slowed down to a crawl. I have run a Mac Cleaner. Other than suggesting a new desktop, any ideas for speeding things up would be appreciated. Should I just reload my old desktop from Time Machine? Is this the end of an era?

THANK YOU