The MQ server image is run using with UID 1001, though this can be any UID, with a fixed GID of 0 (root).
The MQ Advanced image requires no Linux capabilities, so you can drop any capabilities which are added by default. For example, in Docker you could do the following:
docker run \
--cap-drop=ALL \
--env LICENSE=accept \
--env MQ_QMGR_NAME=QM1 \
--detach \
ibm-mqadvanced-server:9.4.0.0-amd64