I'd say to kinda not think about google play system updates.
Basically, every month or so google releases a google play system update, might tweak a few things, might add a new google feature. Nothing giant.
Because these updates are by google, samsung checks them to make sure nothing conflicts with their software.
If you aren't getting play system updates, it means samsung has paused them while they work on a problem.
Unlike normal updates, google play system updates can be months behind with no real downside at all.
Treat them as "oh cool, a new one is out". Instead of something vital you need monthly. It's common for them to be paused for many months.
Your phone should be on one ui 8, android 16. Being on the September security patch would mean you are 2 years out of date.
Getting back to the play one. Your phone will have compatability issues with newer play updates for whatever reason, so samsung paused it at July. Probably because you're a year or two behind on normal updates... Correct me if you actually meant one ui 8 with android 16.
Now, a slightly more worrying part here is why your device is still on one ui 6, it should have gotten the one ui 8 update months ago.
As for your tablet, that also should probably be on one ui 8 or at least one ui 7 by now.
Play system updates aren't something to worry about, being around 2 years behind on full system updates is the worry here.
Apologies if this reply is a bit of a mess. I originally started explaining how play updates can be delayed before I realised your real issue was being years behind on system updates