Yes I didn't think that optimizing was stuck for you, but I was just saying that you could always clear Play Services Cache anyway. I REALLY, REALLY, do NOT think that it's a problem!
When the device has had some changes, especially after any OTAs, it makes sense to me that Optimization is likely going to happen. It's also quite possible that the Optimization does not completely finish in one shot.
I've Reboot 3 times this morning (thanks to you lol) and the Optimization only happened once out of the 3 times.
Personally, I'd much rather see it go through the process, than lay there dormant & gum up the works, as they say 😉
Are you seeing this after EVERY Reboot?
Occasionally, I will see something like, "One UI Optimizing apps" after a Reboot, but not every time.
It's likely nothing to be concerned about, as it is Android just verifying the integrity of the system.
"Phone is Starting" is what I always see after Unlocking, "One UI Loading", could just be what is displayed on the S23 series.
It can also occur if there are out of date apps installed, or if some apps have issues with Battery Optimization on startup.
You could also Boot into Recovery & Wipe Cache, see if that clears it from continuing to happen.
Power off the device & wait a few seconds. seconds.
Press & HOLD the Power & Volume UP buttons until you feel the phone VIBRATE & Release BOTH buttons at the same time.
Wait a couple of seconds until you see the Recovery Menu.
Use the Volume button to scroll down to "Wipe Cache" & Select it with the Power Button.
Wait until the Recovery Menu Defaults Back to "Reboot System Now".
Next time you should probably make your own new post, rather than hijacking someone else's.
Your questions will get more attention & won't be a distraction from the OP's original question 😉