Steradiant's questions

I tried to install wine like described here https://wiki.winehq.org/Ubuntu but I always get the error

winehq-stable : Depends: wine-stable (= 5.0.3~focal)

when I try to install wine-stable (via sudo apt-get install wine-stable) the following error occurs

wine-stable : Depends: wine-stable-i386 (= 5.0.3~focal)

again, going back one step, hence, trying to install wine-stable-i386 I get

wine-stable-i386:i386 : Depends: libfaudio0:i386 (>= 19.06.07) but it is not going to be installed
                         Depends: libgphoto2-6:i386 (>= 2.5.10) but it is not going to be installed
                         Depends: libgphoto2-port12:i386 (>= 2.5.10) but it is not going to be installed
                         Depends: libldap-2.4-2:i386 (>= 2.4.7) but it is not going to be installed
                         Depends: libpulse0:i386 (>= 0.99.1) but it is not going to be installed
                         Depends: libudev1:i386 (>= 183) but it is not going to be installed
                         Depends: libxml2:i386 (>= 2.9.0) but it is not going to be installed
                         Depends: libasound2-plugins:i386 but it is not going to be installed
                         Recommends: libglu1-mesa:i386 but it is not going to be installed or
                                     libglu1:i386
                         Recommends: libosmesa6:i386 but it is not going to be installed
                         Recommends: libsane:i386 but it is not going to be installed or
                                     libsane1:i386
                         Recommends: libsdl2-2.0-0:i386 but it is not going to be installed
                         Recommends: libxslt1.1:i386 but it is not going to be installed

I tried different things recommended here like deleting the repository and adding it again and so on but nothing really worked. I'm using Ubuntu 20.04 LTS. Does anyone have a clue how to resolve these errors?

Edit1 - output of sudo apt update

Hit:1 http://archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://ppa.launchpad.net/pinta-maintainers/pinta-stable/ubuntu focal InRelease             
Hit:3 http://dl.google.com/linux/chrome/deb stable InRelease                                     
Hit:4 https://download.owncloud.com/desktop/ownCloud/stable/2.7.1.2560/linux/Ubuntu_20.04  InRelease
Hit:5 http://packages.microsoft.com/repos/vscode stable InRelease                                
Hit:6 http://ppa.launchpad.net/smathot/cogscinl/ubuntu focal InRelease                           
Hit:7 https://dl.winehq.org/wine-builds/ubuntu focal InRelease                     
Hit:8 http://ppa.launchpad.net/sunderme/texstudio/ubuntu focal InRelease           
Hit:9 http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu focal InRelease
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.
N: Skipping acquire of configured file 'main/binary-armhf/Packages' as repository 'http://packages.microsoft.com/repos/vscode stable InRelease' doesn't support architecture 'armhf'
N: Skipping acquire of configured file 'main/binary-arm64/Packages' as repository 'http://packages.microsoft.com/repos/vscode stable InRelease' doesn't support architecture 'arm64'

I'm using Ubuntu 20.04 LTS and I want to sort files in a file explorer by their extension. I found the possibility of using nemo and sort the files by the Detailed Type but this doesn't really work satisfactorily. I have e.g. some files from MATLAB with the ending .m but some are marked correctly marked as MATLAB file but some are marked as Objective-C source code but they are also plain MATLAB code. Is there any way to sort the files (and folders) reliably by their extension? I'm not tied to any file explorer so any recommendation is very welcome. The two most important features which must be supported are

1. Sorting the files by their extension (highest priority)
2. Showing the whole address in the address line (rather than only those 'blocks' starting at the home directory)

I want to evaluate the PARDISO (https://www.pardiso-project.org/) solver. I use MATLAB 2020b on Ubuntu 20.04 LTS for testing it. When I download the corresponding files and want to run a test, I get the error Invalid MEX-file '/home/<username>/Documents/PARDISO/ipopt.mexa64': libgfortran.so.3: cannot open shared object file: No such file or directory but the .mexa64 file is present. I searched for this error and found out, that I most likely need gfortran3 to run this file but gfortran3 is not supported under Ubuntu 20.04 LTS anymore. What can I do? Is there any other possibility to solve this problem?

I'm currently working on Ubuntu 20.04 LTS but I encountered some problems with the compatibility to older software e.g. even with a lot of searching I wasn't able to resolve the errors for the following command sudo apt-get install swig ipython python-dev python-numpy python-scipy python-matplotlib --install-recommends which gives me the following errors

E: Package 'ipython' has no installation candidate
E: Package 'python-scipy' has no installation candidate
E: Package 'python-matplotlib' has no installation candidate

Therefore, I'd like to downgrade to 18.04 LTS. I think there is no other way than reinstalling 18.04 LTS on my system. My question is now, what is the best way to do this when I still want my Windows up and running. I'm asking because the last time when I installed Linux alongside Windows, I followed the recommendations of a website and my whole system was not bootable anymore. It took me a whole day to get it up and running again. My biggest question is, how to organize the bootmanager. It looks like shown in the picture now. If i read the output of the Grub Customizer correctly, there are two bootmanagers installed at the moment. One on /dev/sdb2 and the other one on / (root)? At startup, Windows starts automatically. If I want to start with Ubuntu, I have to hit the F11 key and choose the 'ubuntu' entry in the start menu. This is a behavior I can absolutely live with.