4G network will be shut by 2026/2027. Not before that. Buying 5G phone makes sense now. But 4G usage will surge after January 2024 as 5G tariffs will be announced. Also, BSNL 4G will be deployed. So let's see. There might be auction next year for 4G/5G spectrum as well. Airtel might want to top up some spectrum in few circles. So let's see how it goes, but buying 5G phone makes sense now.
Better go for a 5G Mobile. Check Samsung or other brand 5G phones, You can get a mobile for around 15k to 20k. Using 5G or 4G signal is your choice! 4G will be here for another 5+ years for sure.