[EmbeddedHash]

Not sure if I understand, but you currently have a device that has UART enabled, and you are trying to communicate with it via BLE? Thus, you want to add a BLE chip, i.e. the nrf52, and then relay the commands from BLE -> UART for the second chip?

Regardless, Zephyr is an RTOS which provides OS functionality like scheduling, interrupt handling, semaphores, etc.

It is most likely overkill for what you are attempting to do. You should instead look at the vendor provided SDK for the nrf52 chip and program it bare metal. The SDK is most likely just libraries/drivers and does not come with an RTOS.

[idank]

Yes exactly. This device is a mini exercise bicycle, it has half a dozen buttons and LEDs with a UART enabled chip that orchestrates everything. I'd like to make it controllable via Bluetooth (e.g. on/off, set speed) and have it send stats like current speed, etc.

Would something like circuitpython not be easier to work with?

[EmbeddedHash]

I would suggest using either an Arduino w/ BLE shield or a raspberry pi pico w. Both platforms have great SDKs and a lot of online support/community. Raspberry Pi pico supports circuitpython if that is the route you want to go (i.e. if you are more familiar with python). But most embedded software is written in C/C++.