unable to create new native Thread or Resource temporarily unavailable after 10K threads

The problem was the systemd cgroup limits...

I checked the "/sys/fs/cgroup/pids/user.slice/user-$UID.slice/pids.max" and it was 10.813. Raised to 15000 and the threads was allocated.

So Systemd uses cgroup to limits resources and threads too...

this post was the path for the truth!

https://askubuntu.com/questions/845380/bash-fork-retry-resource-temporarily-unavailable/883677#883677