Q: Showing string that contains specific number in QGIS How to show all the strings that contain '841' on this layer?

I tried to use "NAME" LIKE '841' but somehow it did not just show "841_1Q" and "841_1", instead it still showed every point on this layer just highlighting those two containing '841'.

I tried using a wildcard but the "Output preview" shows 0 result.

A: It is unclear to me what you want to do exactly. The expression you are using is correct. It highlights the points with the correct expression because you are using "Select By Expression" and the function works exactly as it should be.
If you want to show only those points and hide other points that do not comply with the rule, then you need to use Query Builder from Layer Properties → Source → Query Builder and use the following expression:
"Name" LIKE '841%'

It will hide all points (Polygons in this example) whose field name does not start with '841%'.

However, if you want to show only the labels for those points that start with '841', then you need to select the field name Name, and under Rendering go to Show label, and put the following expression:

"Name" LIKE '841%'

Which is the same as the above.
Here is the output:

