MAX_THREAD_GROUPS 128 setting prevents MariaDB from starting. No configuration is read at the time this check is made. Solution: make allocating the structure dynamic, make default to be always less than MAX_THREAD_GROUPS, or make MAX_THREAD_GROUPS bigger.

./sql/threadpool_unix.cc:static thread_group_t all_groups[MAX_THREAD_GROUPS];
./sql/threadpool.h:#define MAX_THREAD_GROUPS 128
./sql/sys_vars.cc: VALID_RANGE(1, MAX_THREAD_GROUPS), DEFAULT(my_getncpus()), BLOCK_SIZE(1),

Server does not start if my_getncpus() > MAX_THREAD_GROUPS and there is no configuration option around that.