Assign way more replicas than you have of memory on all nodes and watch the Swarm crash which can easily reproduce in a small VMfor testing.
root@Deb11Docker01:~# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAM........
If you have swarm services and dockerd is creating a high load even with the containers just being idle, the easiest solution is to upgrade to a newer docker version.
For example an identical config of 3 nodes, with Redis 5 with 30 replicas produces a load of about 1.45 in Debian 10 with Docker18.09.1
If I create the same setup on Debian 11, with Docker 20.10.5+dfsg1 then the CPU usage is low.
One other difference I wondered is the kernel. In my test setup........