Final Cut is such a mess, help needed

Tom is right. That's not a drive you should be using, at least not in that configuration. FAT32 has a 4GB file size limit, doesn't have journaling, doesn't support macOS file system protections... it's basically what you'd use if you needed to swap Office docs with a Windows user. It's also probably why your footage couldn't be ingested - 4K footage is big.

You'll need to (at minimum) back up your data and reformat that drive, and it'll still be slow.

If you want a far, far better editing experience, I'd recommend getting an SSD and reformatting that (GUID/HFS+ (Journaled)) before using it.

I bought one of these awhile ago, and it's been great:
www.amazon.com/SanDisk-2TB-Extreme-Porta...00-G25/dp/B08HN37XC1

Samsung T7 would also be good. Their T5 series is a bit slower, but still 4x faster than what you've got.

Those little Seagate spinners also don't have a great track record for reliability.

Okay, so as it stands, is there a risk to my project right now? I really can't afford to lose my footage; if I get a new hard drive and transfer it, will there be a difference in quality, or just efficiency and speed?

You shouldn't see a quality difference, but as it sits you can't work with any source files over 4GB. And those drives have a sketchy track record with heavy use.

If you get a new drive (format it first!) and transfer everything, you should be fine. You'll likely need to re-import your footage regardless. If you can swing it though, I would strongly recommend SSD. Your sanity will thank you.