Goblin Engineer appears to have some bugged use cases.

Situation: I had a Blossoming Tortoise (a Hangarback Walker with one +1/+1 counter on it, equipped with an Assimilation Aegis that was currently exiling a Blossoming Tortoise) and was in the beginning of combat step. My opponent activated the "destroy target artifact" ability of their Cankerbloom targeting the Assimilation Aegis. In response, I attempted to activate my Goblin Engineer to sacrifice the Aegis, targeting a Masterpiece Vault in my graveyard. When I got to the step where I could choose which artifact I wished to sacrifice, it brought me to that "these permanents are stacked on top of each other, so choose one" disambiguation screen. There it appeared the Assimilation Aegis was highlighted, but the only button showing was "Done," and I was unable to submit it as the artifact I wished to sacrifice. I clicked done and it brought me back to the "choose which artifact to sacrifice" step. I tried several times to perform the action, clicking on the Aegis, clicking on the Tortoise, but nothing changed, and the "Done" button always booted me back to the previous step in the process. I was unable to submit the Aegis as the artifact I wished to sacrifice.

Expectation: I would expect to have been able to sacrifice the Aegis during this timing window. There were no other permanents or effects restricting my ability to do so. After the Aegis was destroyed I was able to activate my Goblin Engineer as normal and everything functioned correctly.

I'm using a Mac.