As others have said step one is locating where there air is leaking from by rotating the wheel in a big, flat bucket or sink etc.. slowly and looking for bubbles of the leaking air..
Mystery slow leaks like this in my experience (assumption slow leak) has occurred in a few cases
- Tape failure.. usually around valve... or if you replaced the tire, sometimes the tape might get pushed to one side... or nipple hole cuts tape possibly if you didn't double up the tape layers
- Cut right in bead or sidewall.. REALLY hard hits can actually result in snake bite puncture in the tubeless tire itself.. since this usually occurs right in the bead if you put lower pressure sometime it will be able to seal, put in higher pressure and stops sealing.. also just from riding and the cut will open and close and leak air slowly
- There is a hole that is only kinda sorta sealed and the tire will leak slowly over time.. this usually happens with older tires.. if your tire has wet spots on in where sealant is weeping out.. time to change the tire.. running out of rubber..
BUT.. step one.. find the leak.. or your just guessing 🤷🏾♂️