If you queue up construcutors  before selecting starbase expansions, they won't get used for the starbase unless you manually move them to the said starbase. Which I believe then cancels any the starbase actually queued up. If you park a constructor in a starbase orbit, then select starbase expansion it uses the constructor in orbit.

They want to make it less annoying and micro-management but it's turn out to be the most inefficient and obnoxious instead. This is why i won't play with +2 in Capacity and -25% Mass on Construction Modules. Go full ham on capacity increase just to make Constructor management less obnoxious. Use them until it has 1 point left then refit it into another identical blueprint just to get constructor point back. Seriously, i would be gladly to pay the bloody credit to upgrade Starbase.

Too much effort? It's basically a one time setup for each star base.  Compared with manually managing constructors, which is what I thought the OP was talking about, it's a huge reduction in micro management.  I admit it's probably not as efficient as using the upgrade constructor strategy, but then I'm playing this game for what I find fun, and I assume that you are too, which might be different.

If I'm playing on a huge map with 40 or 50 planets, say 5 or 6 star bases per planet (or more), I don't want to manually send constructors to each star base, and then check each turn to see if I have star bases with unused constructors to build with.

As always, your mileage may vary, I've corresponded with people in the past who loved micro-management, and far be it from me to tell them how to play.

It basically only works if you have none thing else to do.

Simply like i suggested before that they hadn't done before where you pick which shipyards sponser the starbase would make it easier. With an option for shipyards to have no sponser. This way i don't have to use all my shipyards for an automated starbases. I don't have to delete constructors from my shipyards. And stardock can reuse what they are already doing with shipyards.

Hyperbole aside, yes I use the feature copiously.  I use upgrade constructors with 2 modules and one of the latest engine. For relics and resources, I use searching constructors that claim anything they find. I am greedy. I have empires of up to 100 planets and I circle planets with econ starbases. I am completist. For planting econ bases, I build a cargo hull with several constructor modules and no drives. It plants a starbase near a nearby planet then moves to build another one until it runs out.  I then cue up 1 module request in all four categories of the econ base.  The econ base then fills itself to current tech levels and I don't care in which order or when. It just happens.

The result is a steady flow/cloud of constructors named 2up coming from everywhere and going everywhere.  I love it.  It is not maximum efficient, but it is manageable and creates a steadily accelerating economy that then builds even more constructors and grows even more.  It is also useful for setting up those newly conquered regions with all those new planets.  Set it and forget it.  I use 2 module upgrade ships because then I can avoid sending a lot of extra constructor modules that sit there waiting for a new tech. For high production shipyards, I cue up lots of the latest warship and fill up their cues.  That convinces the constructor request paradigm to avoid clogging those shipyards with requests. I do not manually edit starbase sponsor shipyards.

I have 2 stages where I research the precursor techs two at a time, which triggers the double constructor upgrade automatically.  I will go through the relics bases and prioritize those module requests, which gets them out of the shipyards and traveling to distant relics much sooner.  Then each upgrade ship gives me a 20% bonus of some kind when it gets where its going. I have done Mining research two techs at a time for a similar little cloud of constructors. Once I was very late in developing Mining and then blasted through the tech branch. Constructors everywhere!

One thing that may be different from other playstyles:  I build lots of low production shipyards at low production planets.  These are excellent at steadily spitting out the occasional constructor that then goes out and does something useful for the empire.  A lot of people only put shipyards in high production situations and let lower production planets concentrate on their research, wealth, whatever. This may affect how well the constructor mechanisms work out for other people.

Yeah, when you capable to stuff your constructor with 3 or more modules then this system wasn't that bad taste but it still not good enough on the early-mid game.