How do I install chromium-browser via apt?
I don’t think you can, on Ubuntu. The Linux Mint devs – which have Ubuntu upstream from them – threw a shitfit about this (see here, for example Monthly News – May 2020 – The Linux Mint Blog).
In mint, I was able to manually install chrome using the .deb from google’s chrome website.
(Then got SecurityError when trying to access usb devices in the web programmer… had to do the udev rules fix documented previously in the thread, too.