For all those who think this is too confusing and have the same problem, the solution summarized:
Problem: display remains white (manufacturer’s driver, destroys Volumio Image); Touchscreen cannot be calibrated
My display: Quimat 3.5 inch touch
Tips: If downloading and copying is too complicated, download this then plug the micro SD of the Pi into the computer and you can easily insert and edit the files.
Solution:
1. Reinstall the Volumio image (not absolutely necessary, but recommended)
2. Open /boot/userconfig.txt
Paste this:
dtparam=spi=on
dtoverlay=tft35a:rotate=90
3. Save and reboot
4. Install the touch display plugin
5. download this here: „ tft35a-overlay.dtb “ download and copy it into „/boot/overlays/tft35a.dtbo" (Don’t forget to rename!)
6.Open “/usr/share/X11/xorg.conf.d/99-fbturbo.conf” and change the options
Option "fbdev" "/ dev / fb0"
to
Option "fbdev" "/ dev / fb1"
then reboot
7.The display should now work
8.In order for the touchscreen to work correctly, it must be calibrated. Create (edit) the file “99-calibration.conf” and add the following content:
Section "InputClass"
Identifier "calibration"
MatchProduct "ADS7846 Touchscreen"
Option "Calibration" "3936 227 268 3880"
Option "SwapAxes" "1"
EndSection
and save it in “/etc/X11/xorg.conf.d/”
9.Change the rotation to 270 ° in the settings of the touch screen plug-in.
10.Everything should work now
The biggest thanks go to, please @gvolt.
He tried everything with me for 2-3 days and supported me very well, thanks to him I can now offer these instructions here.
If there are translation errors, it’s my fault, I’m 17 and come from Saxony in Germany, and I don’t have the best English. Thank you so much for working with @gvolt!! 
