I heard on a podcast hosted by VCs in China that Douyin (TikTok in China) found that an overall ad load of 8% in its short video feed is the maximum without statistically disturbing users. I tried both TikTok and Instagram and found they show one ad every 6 swipes, which amounts to a 16% ad load. I'm not sure if that number is personalized and if the apps happen to detect that I'm more receptive to ads than the average user.