Logseq has a beautiful feature where you can click on a line that connects two bullet points, and it collapses all blocks at the first level.
What’s beautiful about the feature is that it collapses all blocks only at the next level; it doesn’t go deeper than one level.
Suggestion
When you right-click on a triangle next to a block in Obsidian, a menu opens with the following options:
There could be another option in the menu with the same functionality as that in Logseq – so the option to fold/unfold all level 1 blocks.
There could also be a shortcut for this.
eg Clicking on a block-level triangle while keeping Ctrl pressed would fold/unfold all level 1 blocks.