> какой запрос и какой объем выборки?

вот похоже на это, пофиксили на 8.0.27, а исполоьзовалась 8.0.26

Changes in MySQL 8.0.27 (2021-10-19, General Availability)

Concurrent insert operations on multiple tables with full-text indexes caused a large number of full-text index synchronization requests, resulting in an out of memory condition. (Bug #32831765, Bug #103523)

есть и такие фиксы

Some of the functions defined in mbr_utils.cc threw heap-allocated exceptions in some situations. Memory allocated for the exception object in these cases was never freed, which meant that a small amount of memory leaked each time an exception was thrown.

This is fixed by allocating the exception on the stack in such cases, instead. (Bug #104214, Bug #33086286)