On a Pi device, Chromium is installed by default on version 9 (Stretch) and above. To find the version run:
chromium-browser --version
Chromium 113.0.5672.95 Built on Debian , running on Debian 11
To update the browser version run:
sudo apt upgrade chromium-browser
chromium-browser --version
Chromium 126.0.6478.164 Built on Debian , running on Debian 11
What apt does is inspects /etc/apt/sources.list.d/raspi.list and uses the repo there to search for binary packages to install.
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For example: http://archive.raspberrypi.org/debian/dists/bullseye/main/binary-arm64/Packages contains the link to the Chromium browswer
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