I've noticed this with krita 4.1.1 and 4.2.0 pre-alpha appimages.

If I double-click a layer name in the Layers docker, I get an editing window with the layer name highlighted and all the usual text editing characteristics, all working fine.

However, if I right click the layer to get the Layer Properties window then try to edit the layer name in there, I can place the cursor, move the cursor, select text for replacement etc. anywhere in the name but after typing the first character, the cursor moves to the end of the name. This is annoying and inconvenient but not a disaster.

If I edit the name of a bundle in the Manage Resource Bundles window, there is no problem.

Is this a Qt fault (unfixable by krita developers) or does it need a bug report?

report a bug anyway, there's a good chance no developer sees this otherwise (beyond me, that is...)

Bug report made: https://bugs.kde.org/show_bug.cgi?id=398958