That's Chinese Apps for you. I haven't tried TEMU yet, but the typical Chinese App opens a popup on you in what feels like every fucking second. Even something like Baidu Maps shoves an ad into your face every time you switch to another app and then back. It reminds me of early 2000s Internet, before popup/ad blockers.
Going through HN top list today on a machine with no ad blocker I see the same in pretty much all US sites: Cookie popup that is clearly illegal, lots of ads, cookies and trackers (189 on one site), then some JavaScript pop-up about whatever (newsletter mostly) when moving the mouse outside the frame. It is not any better. At most more polished but likely we are just used to it. Good thing I have adblockers in both my normal machines browser and on the firewall.