The Y2K era ended last week of July 2001 in America
Death of Teen pop
Linked an article below discussing the final blow to teen pop. You even had Dirty Pop by Nysnc referencing the "pop life fading out" Christina had already changed her gimmick by the time Lady Marmalade came out. Neptunes were everywhere at this time and they started producing tons of tracks for teen pop acts. Anything teen pop related now needed a rapper to save the song (Nelly in Nsync's Girlfriend or Will Ford I wanna be Bad) That Britney Pepsi commercial that was on tv every 5 min, Nsync in The Simpsons. It was just too much and we were already over it. We were OVER it. Not to mention Shakira and Michelle Branch were getting huge at this time. Nelly was getting huge as well. 2 of them actually! Furtado!
https://ew.com/article/2001/06/08/teen-pop-over/
Fashion
By June 2001 (watch the MTV 2001 Movie awards) fashion had already started morphing in to the stuff we would see in the mid 2000s. Low rise jeans, tons of Air Force 1s, light blue everything. I HIGHLY recommend watching the red carpet of this awards show. Not everything was classic 2000s as some Y2K leftovers were there but you could see where it was going. I also have to add the frosted tips look was already getting backlash and people did make front of you.
Electronics
By now PlayStation 2 had been out for a few months (I couldn't even nab one that summer due to it being sold out) and Game Boy Advance had a very successful launch in America. Apple had starting transitioning it's products from the clear translucent colors to all white plastic. The new ibook commercials that summer had a all white finish to them. DVDs were getting huge and were advertised all over tv for Blockbuster and Best Buy. Sega also dropped out of the console race early in the year and became a 3rd party company. Summer 2001 is when you started seeing more companies establish their base 2000s style and throw sleek curves to the waste bin. Silver electronics kind of became the defacto standard and rounded out with more basic shapes. I remember vividly that summer Best Buy dismantling the Nintendo 64 and PS1 kiosks to make way for Xbox and Gamecube.
Anime crash
We had somewhat of a anime crash in 2001. We had 2 Toonami blocks on at the same time and Pokemon's popularity crashed with the Johto season. The 3rd movie was so bad it was pulled after 3 weeks. Pokemon was never the same after the second movie. Now in general Pokemon is always going to be around and have it's games sold but at this time it seemed like popularity was waning. I am using Pokemon as an example because it was the biggest anime franchise next to Dragon Ball Z (which was doing really good with the Cell saga) You also had Digimon peaking with the second season on Fox Kids and Monster Rancher occupying a small little space. I really think Toonami being on Kids WB! really caused damage to the Toonami brand and anime in general. It was just overkill with anime.
Reality TV
By fall 2000 Survivor had become the biggest show. You soon saw shows like Temptation Island on Fox getting HUGEEE and causing everyone and their dog to produce a reality show.
Sports
Wizards were all in the news due to MJ coming back! It was huge. WCW and ECW also closed up shop. Wrestling's popularity took a major dip due to The Rock leaving for a few months.
Politics/Economy
George Bush took his seat at the top of the year. What more needs to be said? Now at this time while Shark attacks and Dick Cheney's gigantic cock eye were sweeping the headlines we also had to deal with the DOT COM bubble burst. The economy was slowing a bit and tons of internet start ups were closing. Key stores like Warner Bros and Bradlees (North east staple) closed up shop. Supermarkets were seeing a slight dip due to mad cow outbreak. So already the Y2K optimism was fading out.
We didn't exactly know what was coming next, but it was clear it was a slow burn to a new era. To be honest it really did start feeling like the 2000s by the end of July. I remember that week going back to school in August and having it already having a 180 vibe even before 9/11 occured.