Trouble uploading sketch from Arduino IDE

[thedeany]

I'm trying to upload a new version to the theremin I just received last week (I'm trying the MIDI implementation, but this issue also occurs if I try to upload the standard version as in this repo), and I'm getting the following error message.

Sketch uses 27082 bytes (83%) of program storage space. Maximum is 32256 bytes.
Global variables use 362 bytes (17%) of dynamic memory, leaving 1686 bytes for local variables. Maximum is 2048 bytes.
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00
Failed uploading: uploading error: exit status 1

I am selecting Arduino Uno from the boards list in the IDE, and as far as I am aware a "Programmer" does not need to be selected/the programmer choice doesn't matter in this case.

I have updated to the latest version of the IDE, I have tried multiple USB cables and ports, and I've searched for general solutions to this avrdude error, and nothing fixes the issue. Do I need to burn a new bootloader or something? I'm not sure exactly what the process looks like if so.

Any assistance would be appreciated!

Edit: for what it's worth, I just tried a calibration while I had the theremin connected to my computer via USB, and I had the Arduino serial monitor open and I saw the calibration details coming across.