No they won't lose a lot of users, what's the competition or alternative? ChatGPT? Even more AI?

Youtube did like multiple redesigns, each time with massive complaints, clearly had no negative effect on youtube.

Reddit did that huge redesign, and lost like 50% of users initially. Their profits keep going up because they now control the ad distribution and can protect their valuable data from scrapers.

A UI/UX degradation simply isn't enough to turn away free users. You have to damage the fundamental value proposition like say Tumblr banning adult content.