There's an issue with manually supplying a certificate:
adafruit/Adafruit_CircuitPython_Requests#101 (comment)
The NINA firmware limits the certificate length to 1300 bytes. Perhaps the restriction is deeper, but if it can be raised it would help some situations where a longer certificate gets supplied. Otherwise, ESP32SPI gives:
AssertionError: .PEM must be less than 1300 bytes.