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YouTube's ad problem just got worse: Users now seeing 90-second unskippable ads!
(www.androidauthority.com)
This is a most excellent place for technology news and articles.
Seems like youtube forces sign-in using Unwatched on iOS? An alternative is Vinegar which replaces the video player in Safari, and skips the ads, mostly and usually (until youtube updates some things then vinegar needs to catch up).