Your comments

Let us define what a global search is. A global search does include all sections. Thus it is the same as searching in "All". I don't think i want a global search, when i have a section selected and press Ctrl+F. In that case i would need to click the section again, if i want to keep my section selection. As for the thread in the forum, please read my anwser there. Also be aware, that the thread is about global search options (SIW, SAF, sort order).
Shift+Ctrl+F could be added to do a global search. In other words, include all sections to the search scope. Same as pressing Ctrl+Shift+Space when one or a few sections are selected. In case the search scope is "ALL" already, Shift+Ctrl+F should be handled same as Ctrl+F.
Add layout options such as Thunderbirds classical and 3-columns list. That is the tags sidebar, the notes list containing only titles and a preview for the current note's text. The note's text can be either placed beneath the notes list or as a separate column to the right. Also check this thread here
A control at the bottom does require more mouse movement. A control similar to the tag sidebar , placed above the tag sidebar sounds interesting, as it would allow a simple click to switch the database.
I understand your concerns, except some less mouse movement and a unique control, there is little advantage.
Personally the existing features work fine to me. The suggestion is to make the feature available to users, who want to use the UI only, rather than having an ini-file setting. As said, i am fine with the feature. Regarding your concerns it would be another option to make the setting available in the UI. However, my guess is, only a few people are aware they can use the TAB key to focus the search box while keeping the filter, in case Ctrl+F uses automatic clear feature.
Hint: Ctrl+F sets the focus to the search box, regardless of the above setting. The TAB key also moves the focus.
The feature is available with CintaNotes 2.5 by setting filters.reset.onctrlf.enabled = 1 and pressing Ctrl+F in the UI. My suggestion is to make this a natural enhancement, not requiring to tweak any setting. A menu item and a shortcut should be assigned. Currently Ctrl+N is used to create a new note, it could be used to prepare a new search, since pressing INS will also create a new note.