How can I download Google Chrome on macOS 10.15.7?

Many third-party browsers now require Big Sur or better. Not just Chrome, but also Brave (another browser based on the Chromium engine), Opera, and Microsoft Edge.

I believe that the current version of Firefox will still run on Catalina.

Chrome requires Mac OS 11 or newer. The minimum requirements that Google places on all platforms is available here..

https://support.google.com/chrome/a/answer/7100626?hl=en