To repeat:
./mtr --mem --charset-for-testdb=utf8mb4
order_by_all
order_by_icp_mrr
order_by_none
order_by_sortkey

Fix: re-record with explicit charset for queries/tables with mismatch
in explain output.

Also fix:
ds_mrr-big --big-test, use latin1 because utf8mb4 gave plan change.

Also fix: derived, use utf8mb4 except in cases with execution plan changes.