On small screen the sidebar is by default not collapsed and hide the content of the page.
To reproduce simply open https://adminlte.io/themes/dev/AdminLTE/index.html and reduce the window size below a width of 760px.
I would expect that the sidebar will be collapsed by default on small screens (as it was in AdminLTE v2).

https://github.com/ColorlibHQ/AdminLTE/issues/2304#issuecomment-538422237
But I suggest this option should be enabled by default in future releases of v3.
Oh I totally missed this comment.
I can find the option in the documentation (maybe caused by the broken state at the moment).
But after some try & error I found how to set the autoCollapseSize:
Add
data-auto-collapse-size="*"to the<a class="nav-link" data-widget="pushmenu" ...
I would agree with @toxpal that this option should be set by default.
I'll change this behavior like it was before in v2, coming with the next RC (rc.5).
I've changed the default behavior with the latest release (rc.5).
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I'll change this behavior like it was before in v2, coming with the next RC (rc.5).