You guessed correctly. This is only for adding certificates to the radio module on the network connected boards like the Nano 33 IoT. It won't help with allowing Arduino IDE to connect.
I see there was a previous discussion about this subject here:
It looks like it is possible to configure certificates via the Arduino IDE command line interface:
The question is whether that would help with the error you have encountered, which is related to the Arduino CLI tool downloading the file, not Arduino IDE directly. Unfortunately we didn't get any feedback on the subject in the previous discussion.
I do think it is worth a try though. If you do, please let us know what you find.