in the past, when you installed google chrome by downloading the google-chrome-stable_current_amd64.deb package from the google chrome download site, it automatically created a file in /etc/apt/sources.list.d/ to setup a 3rd party repo through which apt can always get the latest chrome version.
for some reason, google has stopped this and no longer provides this repo file. this means, that google browsers in ubuntu will constantly be outdated and ask for re-installation which is not ideal to say the lest.
fortunately, there is still a repo out there, and we can add it manually:
(see https://www.google.com/linuxrepositories/)
wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | sudo tee /etc/apt/trusted.gpg.d/google.asc >/dev/null
echo "deb http://dl.google.com/linux/chrome/deb/ stable main" | sudo tee /etc/apt/sources.list.d/chrome.list
now don't be fooled by trying this url in a browser, google will return a 404 error if the url is entered in a browser, but you will see in the next step, that apt actually gets the files it needs ,so the repo is still working
sudo apt update
this shoud now show the following output between all the other repos:
Hit:4 http://dl.google.com/linux/chrome/deb stable InRelease
now you can install the browser:
apt install google-chrome-stable