In Ubuntu, Chromium is provided as a snap package. The snap subsystem on your computer checks for updates 4x a day. In short, Chromium isn't in any Canonical repo.
I stopped using Ubuntu Desktops when they changed the browsers to snaps. I run Linux Mint on my desktop. Still use Ubuntu Server on the other systems here, well, mostly. Both Chromium and Firefox are shipped by default in Ubuntu as snap packages.
If you want to go outside Canonical supported snaps and use repos from other people, then that is up to you to decide who is and isn't trustworthy.
For firefox, I block the snap package and setup a Mozilla PPA (repo). Additionally, I switched from their 'edge' releases to their corporate ESR releases using /etc/apt/sources.list.d/mozillateam-ubuntu-ppa-focal.list to extend the normal repos. If you google "firefox PPA", you can find reputable articles for how to install the PPA, then how to install the different program packages. This effectively extends the default repos to use those trusted PPAs like they were from Canonical. I figure that the software is already from Mozilla, so using a PPA they curate isn't adding any risks to my systems. I've decided to trust them already.
The firefox version on my systems are:
Code:
firefox-esr 115.8.0esr+build1-0ubuntu0.20.04.1~mt1
firefox 122.0.1+linuxmint1+virginia
I dropped using chromium over the snap problem. Switched to Brave.
Code:
brave-browser 1.62.165
We each have to make our own choices about how much hassle we are willing to have to get a system we'd like. Chromium was a core tool that I used, but with snaps, the way I used it was totally broken, making it useless. I had months to decide and plan. Switching to Mint was the least effort solution for my desktop needs.