Cool. Thanks

Some silicon labs arm MCUs and radios have hardened crypto core and hardened bootloaders. Their closest equivalent to the esp32 is the wgm160p but it lacks Bluetooth and costs more.

Disclaimer: used to work there but this is all public information

How about zigbee products? A few years ago I worked on the development of a wireless product for use in the traffic control industry. Security was of great importance and we opted to use a more costly "low power mcu radio combination" using the TI MSP430 series processors and Anaren radios. At the time we were more concerned with hackers spoofing our radios signals but thinking about it now the physical hacking of our firmware would be just as big of threat.

We use these extensively for our higher security needs, yes it's Microsoft, but it's a great product and solves many problems in this space (Updating, security, etc.)

https://azure.microsoft.com/en-us/services/azure-sphere/