I imagine at least a Linux distribution created by Proton to compete with ChromeOS, which even has a large share in Linux distributions. The Proton ecosystem is there (a Google Docs-style office suite would be missing + the full integration of Standard Notes) and it could be an entry into the company’s hardware? What do you think?
If they had an office suite available there wouldn’t be a need for another OS/Linux distribution imho. Polish the existing products and any Linux distribution should do the trick for you, most of them already are very privacy and security focused.