Having the possibility to choose between automatic placement or not as a default setting

Thanks - an impressive amount of work put in that already, it seems to me!

For the record, I have submitted a PR (code to implement a change) that will add a keyboard shortcut to disable automatic placement, also to make Alt+drag do that automatically, so a future update may include this. It may also become possible o disable autoplace entirely, but the results would normally be pretty bad, actually. Sure, you had to disable it for a small handful of elements, but in the vast majority of cases, it worked so well you didn't even give it a second thought. If it were disabled, you'd have had to do many more manual adjustments to get things looking this good. All those slurs you didn't have to reshape, all those articulations and lyrics you didn't have to move, all those spacers you didn't need to add, etc.

Meanwhile, looking at your score, I see a few things going on where there is room for improvement, either on your part or ours.

Dynamics are a snap to place above vocal staves, no need to disable autoplace or indeed do any sort of manual adjustment. Just press "X" to flip above the staff, leaving autoplace enabled to do its job. Not only is it a ton easier, but it would avoid the collision you other are having with other elements above the staff (or below the staff above) that caused you to need to make yet more manual adjustments. In other words, by disabling autoplace for those dynamics unnecessarily, you created a situation where you needed to make yet more manual adjustments, when everything would have just worked had you let it.

You have a marking that says "about 15" - 20" is entered as staff text, and you are trying to place it on top of a line you entered as a pedal marking. Is that really a pedal marking? If not - and I'm guessing it isn't - it should not have been entered as one. The fact that you entered that as a pedal then flipped it above the staff is part of the source of your problem here. had you simply entered that as a normal line, it would have appeared in the correct place automatically. You wouldn't have had to flip it above the staff, you wouldn't have had to disable autoplace, and you wouldn't have needed to disable it on the text either.

A more general issue is when you try moving elements a long ways horizontally, as MuseScore tries by default to reserve space for the. To some extent you can address this by not attaching the element so far from where you want it to appear, but in other cases, there is little choice. I see that with the images of time signatures you have created. Here, there should be better way. One would be, what if we allowed you to attach images to time signatures? Then you wouldn't need to move them. Or, if we supported the display of these large time signatures automatically. A clever workaround might be to use a staff with invisible staff lines and barlines and set it to 200% scale, but this doesn't quite work.

You've done a fair amount of what seems to me to be unnecessary adjustment. Like, the "bass drum" indication - why are you deviating form the default of left-aligning this? If it's because subjectively you like it offset to appear to the left of the note it applies to, don't accomplish that by manual adjustment do it by adjusting the style setting. One way to do this is to adjust one such marking manually then hit "Set as Style" in the Inspector.

The mid-measure repeat you added shouldn't have needed to be placed as a symbol - instead, you should simply add the barline directly to the staff and note you want it to, using the regular barline on the regular palette. There are some bugs associated with this, but it does work, and it doesn't affect layout when you do the manual adjustment in the same way that using a symbol does.

The vertical space for hairpins is currently fixed at 0.7sp, but in my PR to allow more customization of autoplace it will be possible to customize this setting. So you will be able to set that to 0sp or even a negative value to get a light overlap, while still retaining autoplace and with it the automatic avoidance of the dynamics on either end. meanwhile, you can avoid the extra vertical space without disabling autoplace by using a "staff spacer fixed". Advantage, again, being you still get the benefits of autoplace with respect to the dynamics.

Can you explain the intended meaning of the long horizontal bars int he middle of the staff? A text line with autoplace disabled is indeed a way, but if this is some sort of generalized recognize notation, we could consider supporting it directly.

The staff text you want directly on top of the staff does indeed require disabling autoplace, or at least setting a negative value for the min distance. But again, this is a handful texts in your entire score, compared to the dozens that are placed perfectly by default without you needing to touch them. So, less work to disable it individual where needed than to have off by default and have to do that much more adjustment where autoplace was actually helping.