qmk msys can not convert to get file uf2, fatal error about qmk_firmware

[sigprof]

The oddball/v2_1 keyboard is somewhat odd and not compatible with converters for several reasons.

First, keyboards/oddball/config.h contains #define USE_I2C, but using I2C for split communications is supported only on AVR (this is why you see the compile error). You may try to override that part of the configuration and specify D0 or D1 as the SOFT_SERIAL_PIN; this might work even without removing the pull-up resistors, but the vendor serial driver for RP2040 normally does not require external pull-ups.

Second, the keyboard uses the B0 pin of Elite-C as the CS pin for the sensor:

Unfortunately, all “ProMicro-compatible” RP2040-based boards have the RAW (+5V) power pin at that location, therefore the sensor won't work if you just connect the controller as is, and there is even some chance to damage something because of that connection (VCC is 3.3V on RP2040 controllers). So you would need to avoid connecting that PCB pad directly to the corresponding pad on the controller, and instead add some wire to an otherwise unused controller pin, then redefine ADNS9800_CS_PIN and PMW33XX_CS_PIN to use that pin instead of SPI_SS_PIN (which is defined to B0 when compiling for atmega32u4, but won't be defined when compiling for RP2040).

Also, if you have the “ProMicro RP2040” board from AliExpress (which has a pinout similar to the Helios controller), the proper converter option for it is CONVERT_TO=rp2040_ce. The promicro_rp2040 name refers to the SparkFun ProMicro-RP2040 controller, which does not have the Elite-C bottom row of pins (although the ProMicro-compatible part of the pinout is the same for those boards, by using rp2040_ce you will get the proper USB_VBUS_PIN definition).