Use IMU to determine angular orientation about one axis

I've got a situation where I want to use the IMU-enabled XIAO nRF52840 Sense in order to get the orientation in 360 degrees around the X axis. The answer would seem to be to use either the Z or Y axis acceleration. However, once you cross a certain threshold, the numbers could be + or - in orientation it seems. Therefore, one would need to combine both the Z and Y readings to get an accurate orientation. One idea I had was to use one axis to read measurements, while the other determines + or - orientation. However, I'm guessing there is a standard methodology for this. Using the Arduino IDE, FWIW. Hopefully this is the right place to post, please LMK and/or move if not!
Getting Started with XIAO nRF52840 | Seeed Studio Wiki
Getting Started with Seeed Studio XIAO nRF52840 (Sense)
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