Can't install Update 1803, error 0xc1900204

My computer started trying to install the update at about 3AM every night, despite being put to sleep and overnight being my "active hours" so I decided to try atually installing the update (because I'm still not able to permanently halt updates for some shitty reason).

For nearly a month, every time I try to install the update, it aborts with error 0xc1900204. I have tried running the update troubleshooter, which fixed nothing, and I haven't changed the registry.

I tried with my antivirus...

Can't install Update 1803, error 0xc1900204