Right, the data sheet does not contain any information on this because it is not a device-specific question, but a family-specific one. As I have already written, the information can be found in the reference manual.
Should be possible to walk the part out of RDP via the serial port and ROM based System Loader. With BOOT0=HIGH user code will not run, and not interfere with debug pins/connectivity.
You fail to mention which STM32, as I recall AN-3155 describes the loader commands.
Segger/J-Link used to have a specific STM32 tools to reset/recover the devices into a usable state.
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