Macbook air 2018 crashes and gives "bad magic" system report

Try an SMC reset and PRAM reset (hold the PRAM reset for a full minute so it activates several times -- some models may not allow multiple PRAM resets).

Run the Apple Diagnostics.

Run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper. Allow EtreCheck "Full Disk Access" so that the summaries of the most recent error logs are also included.