@Michal Koch, Thanks for posting in Q&A.
From your description, it seems you are enrolling the Xioami MIX Flip device.
In general, to enroll device via Android Enterprise method, it needs to meet the following requirement:
1, The device model needs to be listed in the Android Enterprise supported list.
2, Confirm Android Enterprise availability in your country or region
After checking the device model in Android Enterprise supported device list, I find Xioami MIX Flip is not listed. Therefore, you will get error device might not be supported while configuring the Intune work profile. You can feedback to Google and Xiaomi support to see if it can be added in the supported list in the future.
https://androidenterprisepartners.withgoogle.com/devices#!?search=Xioami%20MIX%20Flip
Note: None-Microsoft link, just for the reference.
Hope it can help you and thanks for your time and understanding.
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