One interesting fanfiction could be about the secret training regimes within Gotei 13. It might explore how different squads have unique ways of honing their skills that were not shown in the original Bleach series.
I'd suggest checking manga forums or dedicated Bleach fan sites. They often have detailed breakdowns and recommendations on where to pick up after a specific part. Sometimes, the author or official sources might provide cues as well.
I'm not sure of a specific one titled 'Gotei 13 watches Bleach' exactly. But you can look on popular fanfiction websites like FanFiction.net or Archive of Our Own. There are likely many fanfictions that involve the Gotei 13 in some way while being related to Bleach.
Honestly, I don't know when the TYBW manga starts. But you could search manga databases or ask in manga enthusiast communities to get the details you need.