As mentioned by the PRO producers and seen in PIC and DIS, the transwarp conduits left by the Borg post Voyager finale allows other civilian ships to use them as a shortcut between the quadrants. The Kazon seen in Prodigy did that.
Thank the Collective for being so 'considerate' for setting them up so they could assimilate species all over the galaxy (although in fairness, those conduits were a product of collective knowledge of those assimilated species).
At least something good came out of it in part that the Borg created faster ability to travel through the galaxy for everyone.
Huh... perhaps the Agnes Collective also helped create new ones now that they became part of UFP - it would further explain how the conduits continued to exist in the 32nd century (because otherwise, if they didn't have tech to maintain them, they would have eventually degraded and ceased to exist).
My initial guess was that the Kazon stumbled upon one of those Subspace Corridors the Vaduar set up 930 years ago... and because they did extent to Talaxia, it would have made sense that the Kazon would have an easier time finding one and using it compared to say a Borg TW conduit - but then again, the Kazon were deemed as an inferior species, so he may have been ignored by the Collective either way.
However, here's the thing though, the mechanics of how the TW conduits are generated, opened and maintained can be fuzzy - or at least there are couple of methods.
We know the Borg TW network was said to have been 'obliterated' in Endgame... but as we also know and saw, TW conduits can and don't have to be part of a TW hub as seen in Endgame.
Conduits can be independently opened by Borg ships, or ships using a TW coil (such as the Delta Flyer did in Dark Frontier).
Plus as we know, the Lore Borg in TNG set up a number of TW conduits in the Alpha Quadrant (these seemed to have been separate of the main Borg TW hub).
In ST: PIC season 1, we saw there was a TW conduit leading to the Android planet... as such, I suspect that one was part of a smaller network set up by Lore Borg - its also possible the Kazon whom we saw in Prodigy used one entry way from what used to be former Borg space to the one leading to the AQ (we saw a representational graphic in TNG showing Geordi analysing Lore Borg TW conduits... and the graphic said the DQ was the point of origin.
My guess is the Kazon found/stumbled upon that independently set up conduit which wasn't connected to the Hub and survived the 'Endgame events'
In PIC Season 2, we saw a creation of a new TW conduit... and an unusual one at that (however, we don't know if regular [non Agnes Borg] were responsible for it or not.
So, my guess is that Lore Borg initially set up an independent network of TW conduits in the AQ - which the Kazon in Prodigy found and used (along with other species ships). After that, new TW conduits may have started popping up in the 25th century (like we saw in PIC S2).
The Lore Borg TW conduits could have degraded over time though due to lack of maintenance or lack of manifolds to keep them up... or the Lore Borg already set those up and found a way to regulate their shielding without a queen.
PIC s2 ending really set up the storytelling behind that TW conduit (that's one of the good things about PIC amid mediocre story it had), but now we know that S3 (sadly) won't be dealing with that - although, another show might (we may get Star Trek: Janeway series at some point from the initial chatter we heard... so if that happens, it could deal with the TW conduit from PIC s2).
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