Did you tried passing {allowDiskuse:true} option in aggregation??
|allowDiskUse|boolean|Optional. Enables writing to temporary files. When set to true , aggregation stages can write data to the _tmp subdirectory in the dbPath directory.
Starting in MongoDB 4.2, the profiler log messages and diagnostic log messages includes a usedDisk indicator if any aggregation stage wrote data to temporary files due to memory restrictions.|
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