The 32-bit MCU I am using can generate 64-bit true random numbers in the hardware. Can I take advantage of this?
The short answer to your question is, yes:)
You can set an external entropy source to Mbed TLS. In addition, Mbed TLs can be configured to have a hardware entropy source, calling a function implemented by you.
More information can be found in the following articles:
If you are implementing for Mbed OS platform, you can also look at https://os.mbed.com/docs/mbed-os/v5.11/porting/entropy-sources.html
Mbed TLS Team member