I think this is very subjective question. I'm just putting my POV. I've been following tennis since long. I saw the first match in 2003 or may be 2004, although I have picked tennis racquet only once in my life. Just a crazy tennis fan.
According to me these are the players who can make a big impact or I would say they have starting making impact.
Alexander Zverev: The 25-year-old German has already established himself as a top player on the ATP Tour, with 19 career titles, including three ATP Masters 1000 titles. He has also reached the semifinals of the Australian Open and the US Open, and was a gold medalist at the 2021 Olympics. Zverev has a powerful serve and a strong all-around game, and is seen as one of the top contenders to win a Grand Slam title in the near future.
Stefanos Tsitsipas: The 24-year-old Greek player is another rising star in the sport, with 9 career titles and a run to the French Open final in 2021, where he lost to Novak Djokovic. Tsitsipas is known for his aggressive playing style, with a strong serve and a versatile game that allows him to play well on all surfaces.
Jannik Sinner: The 21-year-old Italian has been making waves on the ATP Tour with his impressive play, winning 7career titles and reaching the quarterfinals of all the grandslams. Sinner has a powerful game, with a strong serve and forehand, and is seen as a potential future Grand Slam champion.
Carlos Alcaraz: The 19-year-old Spaniard has been making headlines with his impressive performances on the ATP Tour, winning the US Open in 2022 and winning his first ATP title in Umag. Alcaraz is known for his aggressive baseline play and his powerful forehand, and has been compared to Rafael Nadal due to his playing style and his Spanish heritage. He has recently gained the Rank 1 in ATP (Sept 2022) and as of 20th March, 2023 latest ranking he is number 1 player in the ATP ranking.
These are just a few of the young players who could be considered as the next generation of tennis stars. Of course, there are many other talented players who could also make a big impact in the sport in the years to come.