The "Timer Prescaler Select" portion of GTCR should be 3 bits [26..24] per the datasheet, but the header file says that it's 4 bits [26..23]:
https://github.com/arduino/ArduinoCore-renesas/blob/00910fde8314e299a737f617a2c7cbd727b3a545/variants/MINIMA/includes/ra/fsp/src/bsp/cmsis/Device/RENESAS/Include/R7FA4M1AB.h#L5219
__IOM uint32_t TPCS : 4; /*!< [26..23] Timer Prescaler Select */
Compare to the RA4M1 group datasheet (page 417).
I did some testing and found that the prescaler works as expected if you shift the value to the left by one bit, and that the value written to b23 cannot be read back. More detail in this forum thread.
The "Timer Prescaler Select" portion of GTCR should be 3 bits [26..24] per the datasheet, but the header file says that it's 4 bits [26..23]:
https://github.com/arduino/ArduinoCore-renesas/blob/00910fde8314e299a737f617a2c7cbd727b3a545/variants/MINIMA/includes/ra/fsp/src/bsp/cmsis/Device/RENESAS/Include/R7FA4M1AB.h#L5219
Compare to the RA4M1 group datasheet (page 417).
I did some testing and found that the prescaler works as expected if you shift the value to the left by one bit, and that the value written to b23 cannot be read back. More detail in this forum thread.