For example, the RP2350 is a $1 MCU that includes 2x ARM Cortex-M33 cores or 2x Hazard3 RISC-V cores running at 150 MHz.
The RISC-V cores have M-mode and U-mode, and a Physical Memory Protection unit.
The ARM cores have a Security Attribution Map and an Implementation-Defined Attribution Unit which tags accesses to devices like GPIO/PWM/ADC/... based on the security level of the code performing that access. It also has 2 Double-Precision Coprocessors for each ARM core, one for secure and one for non-secure code. It also has secure boot support if you run its cores in ARM mode.