Build 423 didn’t show in my update either. I went to the download link given when it was announced.
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MacBook Pro 2020 - Big Sur 11.3
BiaB UltraPak+ 2020 Mac, (423)
Yamaha SLG200N
Epiphone Les Paul Studio

Logic Pro X,
Xtra Styles 1 - 10. Loops-with-Style PAK 1 & 2. Multistyles PAK 1.