Can I upgrade my iMac running macOS Catalina to latest OS?

If your 27" iMac has a hardware model year of

• Late 2012 or Late 2013 – Catalina is the end of the line
• Late 2014 or Mid 2015 – Big Sur is the end of the line
• Late 2015 – Monterey is the end of the line
• 2017 – Ventura is the end of the line
• 2019 or 2020 – You can upgrade all the way to Sequoia

How to download and install macOS - Apple Support

What is the exact year model of that iMac..?

see > Identify your iMac model - Apple Support

You would need a 2019 or later iMac to install Sequoia.

You are "end of the line" with Catalina. No way around that.

You may want to install Firefox . I believe that the current version will run on Catalina. The current version of Safari only runs on Macs with Ventura or better.