How can summon a stationary mob?

Solution 1:

Unfortunately, there are no NBT tags on Minecraft Bedrock, but two of those three are possible to do with commands. While you can't remove a mob's AI, you can keep it in one location by placing an always active repeating command block with the command tp @e[type=<entity_name>] <x> <y> <z>. For example, tp @e[type=zombie] 0 4 0 which on a superflat world would keep the zombie in place at 0, 0.

To make an entity invulnerable, you need to use /effect. For the zombie, use effect @e[type=zombie] resistance 1000000 255 true. This will apply Resistance 255 to the zombie for 1000000 seconds without particles.

I am unaware of a way to make any entity silent through commands, unfortunately, but at least those two are able to be done.