70 seconds seems a lot, it’s not what I had on my iPad Air 3.
I took the same mesh as yours and I got ~10s by trimming a small part.
The reason why it’s lagging so much is because Trim needs to fill all the holes (and since the vertices are not weld, there’s a lot of weird things considered as holes).
To make it worse if “screen space boolean” (trim settings) is checked, the whole are filled in a special manners, that fails miserably if the hole are not aligned with the camera (in a nutshell the filling only works correctly for the hole created by the Trim itself).
Anyway, this is just one of the many reason why Nomad merge vertices.
I disagree, it should and will be activated by default.
There’s no threshold when detecting duplicated vertices, the vertex needs to be strictly equal.
It normally cannot happen inside Nomad.