How do I turn *off* the input shaper?  

RE: How do I turn *off* the input shaper?

The only way I'm aware to disable it is from the printer menu.  I highly doubt it's at all related to the quality issues your having.  All input shaping does is compensate for unwanted movements related to the kinematics of your printer.  If you want to slow it down I recommend doing that in the slicer by reducing the volumetric flow rate in the filament settings to a level that you deem acceptable. 

Maybe also attach some pictures of the issues your having.

RE: How do I turn *off* the input shaper?

There are unfortunately a lot of variables.

My MINI was broken from last July though about 2 weeks ago (broken y-axis stepper motor, just took me a while to find the time to disassemble/reassemble it.)

When I got it back online, I upgraded the PrusaSlicer from 2.6.?? to 2.9.0, and then almost immediately to 2.9.1.  At some point it downloaded a bunch of new printer definitions which included the Input Shaper designation.   Shortly thereafter the bowden tube failed, and my attempt to build a new one went sideways and the replacement ended up 2x as long as it should.  I ordered a replacement from Prague, but it only arrived today, and I haven't had a chance to replace it yet.

Several things changed about about my sliced/generated gcode since I got the printing running again, even before the problems with the bowden tube. The temperature ranges for "Generic PLA" went from 215/210 to 230/225 C, the print speed went *way* up, and the quality went down considerably.  (also the purge strip at the beginning of the print went from right->left to left->right, but I doubt that's an issue, just a sign the stuff has changed.)  The problem is that I'm having excessive stringing and overextrusion, the precision of printing has gotten a lot sloppier.  I've seen a lot of people on here complaining about similar problems since the PrusaSlicer 2.9.x upgrades and the 5.x firmware release, and a number seem to implicate the Input Shaper changes, though I guess it *might* be the speed increase that came along with it.

The overextrusion/stringing might be due to the wacky bowden tube, so I've increased the retraction from 2.5mm to 5.0mm, but that hasn't changed the behavior.  What I have noticed is that the old gcode sliced before everything changed is still printing well, it's only the stuff sliced since the changes that seems to have trouble.So I'd like to see if I can back out those changes in the slicer configuration, but it isn't obvious how to do that, other than just re-install the old packages (not even sure that would work, since the profiles that would be downloaded from prusa3d.com would still have the IS configuration?  The profiles I can find no longer have a option that *doesn't* mention the input shaper, and I'd like to back that out as well.

I'll try to get some apples to apples comparison pictures tomorrow.