I took a quick look through, but I have not done much with I2C on the UNO R4
I know there are a few open issues with Wire on these boards.
Like:
Wire::setClock() only allows exact values of 100kHz, 400kHz, and 1 MHz · Issue #68 · arduino/ArduinoCore-renesas (github.com)
But my quick look through I believe it is using 400000 as the clockspeed.
Wire clock is slow for some 3.3V devices. · Issue #69 · arduino/ArduinoCore-renesas (github.com)
@Merlin513 - I doubt you have this board either. But wonder if you have any other ideas?