I'm afraid I don't have enough expertise to help here.

Searching for enqueuelocation in the scripts, there are a few examples that probably will work better. My immediate concern is that this may block enqueuing if any empire has one enqueued, not just yourself. See https://github.com/freeorion/freeorion/blob/master/default/scripting/buildings/STOCKPILING_CENTER.focs.py#L37 :

        & Number(
            low=0,
            high=0,
            condition=(
                Planet() & Enqueued(type=BuildBuilding, name="BLD_STOCKPILING_CENTER", empire=Source.Owner, low=1)
            ),
        )

though I think the low=0 and low=1 are unnecessary there.

may block enqueuing if any empire has one enqueued, not just yourself

Sounds 100% likely.

The Imperial Entanglement Center is a bit over the top not only with the low=, but also - how is one supposed to have one enqueued somewhere that's not the capital? Not through losing the home planet by conquest, nor by building the indepencence decree... A mix of quitting, changing the rules, then reloading might do it...

Comparing the "why can't I build this" tooltips before and after your suggested change....

Before:

... note the double blank between "empire" and "has". And I did sloppily read that as "where the empire has".

After:

... better. Good catch.

The where empire has between thing is also a bug in the description generation code for the Enqueued condition. Currently it doesn't handle the case where no empire ID is specified, even though the condition Eval function does.

Probably the behaviour difference is more important that that, though...