There once was a
better-i2c development branch I started in 2017 which allowed - among other things - to send and receive I2c messages from within Pd. I rebased it twice already to bring it up to speed with the rest of the Bela core. Following your request, it's time for the 2022 edition of better-i2c-rebased: better-i2c-rebased-2022.
If you update your board to this branch (following the instructions here) you can then open the example PureData/i2c to write/read I2c messages from within Pd.
As an aside, there exists at least one Pd external that allows to do I2C I/O. However, like most of Pd core and external, this performed I/O from within the audio thread, which is bad practice when dealing with real-time processing.