already installed lap, but the warning message shows:
Warning: Unable to use JDE/FairMOT/ByteTrack, please install lap, for example: pip install lap, see https://github.com/gatagat/lap

Solution: check your version of lap by 'pip show lap', my version is 0.4.0, then check your numpy version by 'pip show numpy', make sure your numpy version is 1.21.2, if not, use 'pip install numpy==1.21.2'. Then the problem might be solved.