Infineon 60GHz IoT FMCW radar modules have all datasheets published. That's super rare for Infineon - usually they are the worst NDA-hell on earth.

Chinese vendors sell uC+Radar-Module units on Aliexpress for around ~20-30€. They Infineon-based boards are super easy to spot by looking at the Antenna-on-Chip layout.

You can cut off their head (microcontroller) and directly attach your favorite uC onto the SPI bus to talk to them. Or use the existing one.. not overly complicated to reverse engineer the schematic.

Example: MicRadar RA60ATR2