Thankfully it looks like mysql is deprecating this so hopefully wordpress will also stop using it.
The SQL_CALC_FOUND_ROWS query modifier and accompanying [FOUND_ROWS()](https://dev.mysql.com/doc/refman/8.0/en/information-functions.html#function_found-rows) function are deprecated as of MySQL 8.0.17; expect them to be removed in a future version of MySQL
I've seen issues with FOUND ROWS where it sometimes doesn't select the correct query to convert to a count()
Mysql docs: https://dev.mysql.com/doc/refman/8.0/en/information-functions.html#function_found-rows
Thankfully it looks like mysql is deprecating this so hopefully wordpress will also stop using it.