For the past year, Steam has been adversely affecting users with migraines, epilepsy and vertigo. Look it up and you'll find plenty of references. Some people affected have easier workarounds that involve still using the new client but with specific settings, while others have only been able to safely work around the problem by reverting to an older client version, which Valve have blocked from being an option since the end of May and beginning of June.
No, that steam community page is NOT unavailable, I just checked by loading it incognito to ensure it's not using a cached version and it's definitely still there. There are also several others on the topic. Here, have a different one:
https://steamcommunity.com/groups/SteamClientBeta/discussions/3/1658943116231004...
Sorry this was the other one:
https://steamcommunity.com/discussions/forum/10/1745643015563656613/