Release 0.21 tracker

[NicolasHug]

Branch cut was made this morning.

Branch
Hud
Current Status PR

[NicolasHug]

CP: #8799
Category: docs
Status: merged

[NicolasHug]

CP: #8800
Category: io feature
Status: merged
Note:

I created the release/0.21 a few minutes before I landed #8671 on main, so this needs to be cherry-picked. This is by design: I need to closely monitor any potential issue with that specific PR, that's why I didn't land it on main before the branch cut. So, this is definitely not a "last minute rushed cherry-pick", it's 100% supposed to be part of this release, and having it as a CP helps debugging any potential problem.