2) You don't actually need to build a browser to achieve this goal, you just need a root program, and a viable (to some extent) substitute already exists. cf. all "Qualified" stuff in EU lingo. So again why do the work and risk spectacular failure if you don't need to.
3) Building alternative browser for EU commerce that you'd have to use for single market, but likely wouldn't work for webpages from other countries would be a bad user experience. I know what I'm sayig, I use Qubes and I've got different VMs with separate browser instances for banking etc. I'm pretty sure most people wouldn't like to have a similar set up even with working clipboard.
There are things you can't achieve by regulation, e.g. Galileo the GPS replacement, which you can't regulate into existence. Or national clouds: GDPR, DSA, et al. won't magically spawn a fully loaded colo. Those surely need to be built, but another Chromium derivative would serve no purpose.