Pressed 1 or ` now mesh is gone I think I hid a mesh (named &quot;rims&quot; in attachment) and then created a cylinder. After accidentally hitting 1 or ` (I'm not sure) the cylinder is gone even though appears as showing in the scene.
Alt + H doesn't work; cannot even bring the hidden mesh back.

Alt + H or toggling the eye icon does not make mesh 'rims' or 'cylinder' visible.
How can I view meshes again?
When you press the 1 key in object mode, it hides all the collections except the first one. Likewise, if you press 2 it will hide all the collections except for the second one, and so on.
To unhide a collection click the eye icon to the right of the name of the collection.