I've tried power cycling and a factory reset my Helix modem to no avail. Only IPv6 supported websites are currently working for me such as some Google, Microsoft & Meta associated websites, some of Videotron's (such as the forum) and miscellaneous websites. Other services such as Steam (& video games), Amazon and Outlook on IPv4 cannot be accessed.
If this situation only affects one computer, I recommend making sure that IPv4 is enabled in your computer's network settings. If the situation affects multiple computers/mobiles/tablets, this could be an issue with the configuration of your network.
Are you using the Helix gateway only or do you also have a personal router in addition to the gateway?