iMac not working properly after Big Sur update

Hi! I don't know how to properly explain this, because I'm honestly really frustrated and scared that one of you is gonna say I need to go to the Apple store and/or possibly lose everything on my iMac, but here goes nothing.

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So the other day, on Friday, I decided to finally update my iMac to the Big Sur update after weeks of avoiding it. I knew it was going to take a while, as it was 12GB, so I left the room to let it update on it's own. I had heard many people had issues after the update, but I usually never have issues after any updates, so I wasn't thinking there would be any problems. So I went to sleep that night, then the next morning/day I saw that it had frozen on the Apple logo screen at some point, half-way into the update, I believe.

So I restarted it, and left it alone once again for a while, came back in the room and saw that it said "An error occurred while applying the software update" and it seemed like either the screen was frozen, or the mouse wasn't working/wasn't connected to the bluetooth. So I restarted again, and got the same results. After several restarts, I finally broke down and did the NVRAM/PRAM reset, held the keys for 20 seconds like suggested, and now whenever I turn on my iMac, it's in a constant reboot loop that I don't know how to stop or fix. In other words, it turns on, loads up, and half-way into loading up, it shuts off and turns back on, and repeat.

The only other thing I've tried to do is put it into Recovery Mode, but the problem with that is, I can't click or press anything. My keyboard and mouse aren't connected to bluetooth for some reason, and I also notice the WiFi no longer connects. I connected my keyboard with a USB and that works, which is how I got to choose the language to English, but the mouse still isn't working. So my only option I'm thinking now is to buy a wired mouse just to at least get past Recovery Mode, pick Disk Utility or whatever, and move on from this, but I honestly don't want to spend money like that if I don't have to. But I seriously am lost on what else to do. I'm scared that I screwed up my Mac by doing the NVRAM/PRAM reset. I was just trying to update my iMac, because I knew the longer I waited, the longer it would take due to the amount of updates it probably needed, so I figured I'd get it out of the way.

The last step now I guess, is maybe go to the Apple Store, which I'd have to book an appointment due to COVID-19 and they're currently not accepting walk-ins. But I haven't went or done it in years and I'm worried that they'll give me bad news and that I need to completely restore/clear my iMac, which I mean, wouldn't be the end of the world, because I have a 4TB Seagate Expansion Drive that has 2TB left of storage, but it shouldn't have to get to that point.

My apologies if that was insanely long, but I don't know what else to do, so I figured I'd come here and post about it. Any tips?