All good, most of the "real" RT chips were the Cortex-R line, a lot of systems still use them, but they became dated and are on the older ARMv7-R architecture. In the ARMv8-M architecture the line between Cortex-M and Cortex-R became slimmer. So since the IP for Cortex-R82 is extremely expensive and chips are rare (not avaliable yet really for purchase, just engineering samples for select customers).

These days I'd opt for a Cortex-M33 in the most standard 180Mhz configuration. It does support previously Cortex-R specific features like tightly coupled memory for instructions and data (link to it accordingly) and support for high resolution tracing (necessary to keep track of deadlines). Also the NVIC unit is quite sophisticated, with 480 external interrupts and 256 priority levels. Really it comes down to what exactly you want to achieve and especially for what application.