I don't know if this is a problem or whatever with either IDE or Teensyduino or both.

I have been struggling with a Teensy 3.2 and my new Teensy 4.0 for a couple of days now.

The sketch is known to be working in the past so i can only suggest it is a software issue.

Under the latest environment, 3.2 version will not compile and states error after error with the ADC commands.

4.0 can't or wont find the correct libraries for the project

I have now overcome both issues i believe but it was a faff

For the 3.2 i had to roll back to IDE 1.8.9 with Teensyduino 1.48b1 worked 1st time?

For the 4.0 i had to delete various libraries for RA8875 and paste the required library into the RA8875 library inside arduino/hardware/teensy/avr/libraries/RA8875 overwriting its contents

this allowed me to compile and upload to the t4?

i haven't as yet tested t4 operation within its project


hope this helps someone