MCUs refers to all sorts these days.

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.

8-bit parts are still around, but the cost savings often isn't worth it for smaller volume production compared to 32-bit MCUs. Easier development saves a lot of money. 32-bit parts are dirt cheap, and the varieties with built-in WiFi or Bluetooth or such are usually cheaper than separate MCU + radio + development to integrate the two. 8-bit flip-chip parts are even cheaper, but the bill of materials (BoM) savings aren't big enough to pay for the added engineering effort to use them for anything but the simplest tasks or the biggest volume products.