MacBook Pro Big Sur Disk Space Not Properly Allocated

When I list my available Disk Space, I see that I should have around 466Gi available to me. However, only ~23Gi is actually available.

df -h
Filesystem       Size   Used  Avail Capacity iused      ifree %iused  Mounted on
...
/dev/disk1s1    466Gi   21Gi   33Mi   100%  553789 4881899091    0%   /System/Volumes/Update/mnt1

FULL OUTPUT AT THE TIME

Why is this the case and what is the best way to fully allocate the Available space?

When I list my available Disk Space, I see that I should have around 466Gi available to me.

I'm not sure where you are getting this from.

According to the full df -h output, you have 435 out of 466 GB used on your Data volume, and most of the remainder of the space is taken up by the system. You should only be seeing 2.5GB free right now, which is well below the recommended 10% and puts you in danger of running out of space due to temporary files or VM swapouts. Sounds like you need to delete some of your 435 GB ASAP.