One more note to ensure success in making the web gui features work in ROOT. It is important to install the ‘chromium-browser’ and not just ‘chromium’. This is (at least in part) because ROOT searches for the ‘chromium-browser’ application but does not look for ‘chromium’.
Practically speaking on Ubuntu on WSL2, this means you should not install chromium directly using the ‘snap install’ command. Rather, use ‘sudo apt install chromium-browser’ and this will install the snap version of chromium but also enable the name ‘chromium-browser’ that is needed by ROOT.