Just a heads up to anyone upgrading from Ubuntu 18.04 to 20.04 and things don’t go well. I am posting this because It was not easy to find an answer online.
Today I upgraded as per stated above.
In Ubuntu chromium is now using snap. In 18.04 I was not using snap. The transition is supposed to go smoothly, but it didn’t. I was missing all of my years and years worth of bookmarks and most importantly my saved usernames/passwords because I did not have sync turned on.
In any case, in my situation I decided to copy over my old profile to the new snap profile location using this command below;
cp ~/.config/chromium/Default/Login\ Data ~/snap/chromium/common/chromium/Default/
I suspect in the end you could have cp -r the whole old profile to the new location like this.
cp -r ~/.config/chromium/Default/ ~/snap/chromium/common/chromium/
I hope this helps someone somewhere