ok, I know I said I wasn't going to comment further, but, well.. I am female and entitled to change my mind, LOL
Slic3r does not create the best supports in most cases.. they are ok for some things, but in general, eh..
that is something the developers need to work on.
for "custom" supports, use Meshmixer.. you can add & remove support structures as you see fit. It will also analyze the model and color code what it thinks could be problem areas so you can decide if you need support there or not. Meshmixer supports will also break off pretty cleanly - even when using TPU. I was actually pleasantly surprised by how well they came off of the TPU - was not expecting that.
I have been doing this for several years now... started with a used Solidoodle 4, Repetier Host and the built in version of Slic3r - there was no S3D then. I learned how to properly calibrate, and how to properly use Slic3r to get the best results possible. basically, I cut my 3d printing teeth with Slic3r. It works, it works well when properly set up, and it is free.
I still own that 1st SD4, and use it regularly - it is my "go to" machine because it is so reliable and so well calibrated, and I have added a 2nd one as well - almost as good as the first one.
Chris has known me since before the FT-5 became available.
I have built three of the Folgertech kits, and still own 2 of them... Started with the 2020 Prusa i3, built it, modded it, then eventually sold it as I am not a fan of the Prusa style movements. The person I sold it to used it to death, rebuilt it, and used it some more. He still has it as far as I know.
I then built the Kossel Rev B kit - still have that one, although it does not get used much. It is a solid kit and was a worthwhile learning experience.
and finally the FT-5, initial release... still have it as well, including the CNC add-on kit - which frankly, was a nice idea, but kind of fell flat in implementation - the parts are fine, but controlling it is/was an issue.
I also have a beta testing machine from another company - that thing is a beast! rock solid, heavy, and fast. It is a CoreXY, Duet 32bit board based monster that I have a love/hate relationship with.. Love the machine, Hate having to use S3D with it, but that is what the developers want used, so...
So, if you ever want help in setting up Slic3r properly, just ask. Not saying I know every single thing about - i learn new tricks with it myself from time to time - but I do know it well enough to get you set up properly with it and produce very nice results.
To give you an idea of how well I have it dialed in... this was printed in Hatchbox Gold ABS (most use PLA for this guy - not me, LOL)
or this... also done in ABS, with TPU jaw pads
Printed Machine Vise