We migrated our mongodb server from AWS r5d.16xlarge to r6gd.16xlarge (Intel Xeon Platinum 8000  -> AWS Graviton 2) and faced with significant performance degradation.

Performance degrades in case of many parallel queries of any nature (we noticed degradation on aggregation/distinct/filter queries, so, don't assume that issue is related to kind of query)

On the screenshot below red metrics for two same databases in the one ReplicaSet, the green one is ARM(r6gd.16xlarge), the yellow one is x86_64(r5d.16xlarge), the vertical red bar is the point to a time when we switched primaries (from ARM to x86_64). Our clients reading only from primaries. How you can see, under the same kind of load produce 100% load on the ARM server but ~10% load on the x86_64 server. Load is constant within a day.