Okay, I believe I may have pinpointed the issue - AT&T users have been reporting possible outage issues for the last several days - this may be the case for you. This was happening to me before, not to the same level, but stuff not loading constantly, things being slow and clunky, and it turned out my ISP was having outages all week that I'd been having the issues.
I gave it a few days and a lot of the ping and latency issues stopped.
However, you may also have to do some internal work yourself:
1. have you tried defragmenting your hard drive? if not, you should do that.
2. (kind of basic but doing this helped with my overall pc speed immensely) clean out your fans with a can of compressed air if they're looking a tiny bit dusty.
Alternatively
3. It may *actually* have something to do with space, normally when PCs start running out of space things get a bit wonky. See if you can't get an external SSD or HDD (2 terabytes HDD will set you back around $50-60 USD, a 1 tb SSD will set you back about $150 give or take ten or twenty bucks, pros of an SSD: you'd get more speed out of your storage, HDDs are a bit outdated in how they deliver information. Things will load faster, take less time, your PC will probably go from taking 30 secs-1 minute to boot up to taking like 5 secs)
4. Worse comes to worse, save all of your necessary files onto an external drive, like a flashdrive or external HDD/SSD and do a full reinstall of windows to your laptop. Normally you don't have to do anything outside of going into "Updates & Security" > "Recovery" > "Reset this PC" and choose a full reset, where it deletes all your files (which is why I recommend saving everything you need onto an external drive OR on something like google drive). Then when it's done, don't redownload anything other than your preferred internet browser and ffxiv, see if that fixes it. If it does, then slowly start downloading your other programs - after each program, run ffxiv and try to log in and if you get the infinite loading, then you've narrowed down the issue.