Yup.
In tech-speak there is 5G NSA (Non-Standalone Architecture) and 5G SA (Standalone Architecture).
5G NSA is a kludge, it is 5G radios operating on a legacy 4G core. Inherently backwards compatible.
5G SA is 5G radios on 5G core. Clearly not backwards compatible.
5G SA is the preferred route for good reason:
1. It delivers reduced power consumption at both operator and user-device level
2. It delivers improved latency and bandwidth at both operator and user-device levelIf you're building new towers, things change, obviously. That said, a lot of industrial/IoT hardware still requires 4G so it's not entirely unreasonable to deploy 4G in new coverage areas.
MSR base stations are the norm in the industry, not a rarity.
5G RedCap is the solution, but that will need new infrastructure and chipset. LTE will stay at least for another ten years.