After upgrading to F37 with GNOME 43, I cannot preview files using the spacebar button in Nautilus anymore. The files highlight just appears and disappears.
However, manually running sushi /path/to/file still previews the file correctly.
It’s fine to discuss pre-released versions here, but you’re more likely to get up to date information on them with the QA team, since their job is to test these on a regular basis.