[Samsung Galaxy S21 Ultra] bANONYMOUS:
Just relax, take a breath, make a coffee, don't take it to heart. Everyone is an asshole on the internet. @Jay5583 probably just stubbed their toe and was pissed off at the world so they lashed out at you.. Or they just clearly didn't know there is a typo in the opening post. It says that Beta 1 for G998U is AUH9 to ZUID, which is not true. It's AUGQ to ZUID. AUH9 is ONLY for "U1" and does not exist for "U" (which is why it would seem like such a simple task to just tell people to search instead of actually helping, because finding a firmware is a fairly simple thing to do, and if people won't help themselves than why help others) but they CLEARLY didn't know that AUH9 doesn't exist for "U" because it's a "U1" only firmware which is why you're not finding anything, because no matter how hard you search, you're not going to find a firmware that doesn't exist lol. So, don't take it to heart that they were coming across as rude because from the information provided on here, it seemed like a very simple task and they were probably just pissed about something else and lashed out at you for asking such a simple question. But the real issue was the typo and the firmware you as well as they thought you needed, doesn't actually exist.

I'll try to explain why it's AUGQ. If you download that file in the first post with all of the links, you'll get a .bin file. Change .bin to .zip, and you can open it. Navigate to META-INF > com > google > android and in there, you will see update-script. If you open this file with notepad or something, you can see on line 5, it says

ui_print("[FEN] source: samsung/p3qsqw/p3q:11/RP1A.200720.012/G998USQU4AUGQ:user/release-keys");

The key part you want to pay attention to is the full build string G998USQU4AUGQ, or rather the last four characters "AUGQ".

This is the SOURCE it's looking for, so when you flash this update file, it will look for that EXACT firmware. If it does NOT see that, it will fail at 47% as so many people on here have seen because of that last U1 Beta 4 upload being the wrong link. (It was for Beta 3, so everyone was failing at 47% because the Beta 3 file everyone downloaded thinking it was Beta 4, it was actaully Beta 3 looking for Beta 2 firmware as the source to flash over top and upgrade to Beta 3, but everyone's phone was already on Beta 3 as the source, so because it was on the wrong source firmware it couldn't flash).

So once you are on the SOURCE firmware, so for G998U, the source needs to be AUGQ, then you can flash Beta 1 for "U", and flash right over top of that Beta 2/3/4 and you're good to go. Maybe do a factory reset after AUGQ to Beta 1 just to assure full stability by removing all One UI 3.1 lingering files that could be in the background and cause stability issues.

@DoctorNasty will eventually fix this typo in the opening post whenever they have some free time so that Beta 1 for G998U is AUGQ to ZUID, not AUH9 to ZUID.

I've already found the firmware you need, and uploaded it to my Google Drive to make your life a little easier

G998U AUGQ

I've also written a full guide here if you need any help along the way. I've covered everything as well as some troubleshooting and other notes and links.

And I have a video guide on YouTube here if you need to see the process first hand if you're more of a visual learner or want to ask questions in the comments or anything.