Ubuntu 18.04 Can't upgrade because of libpython3.6 version conflicts

After having updated to Ubuntu 18.04, when I try to upgrade my system via

sudo apt update && sudo apt upgrade

I get this:

Reading package lists... DoneBuilding dependency tree       Reading state information... DoneCalculating upgrade... DoneThe following packages have been kept back:  gdb gir1.2-peas-1.0 libpeas-1.0-0 openshot0 upgraded, 0 newly installed, 0 to remove and 4 not upgraded.

Of course I tried sudo apt install -f without success:

$ sudo apt install -fReading package lists... DoneBuilding dependency tree       Reading state information... Done0 upgraded, 0 newly installed, 0 to remove and 4 not upgraded.

One suggested solution was to install each separately, but that doesn't work either:

$ sudo apt install libpeas-1.0-0Reading package lists... DoneBuilding dependency tree       Reading state information... DoneSome packages could not be installed. This may mean that you haverequested an impossible situation or if you are using the unstabledistribution that some required packages have not yet been createdor been moved out of Incoming.The following information may help to resolve the situation:The following packages have unmet dependencies: libpeas-1.0-0 : Depends: libpython3.6 (>= 3.6.4~rc1) but it is not going to be installedE: Unable to correct problems, you have held broken packages.

So I tried to install libpython3.6, which doesn't work because

 The following packages have unmet dependencies:   libpython3.6 : Depends: libpython3.6-stdlib (= 3.6.5-3) but 3.6.5-5~16.04.york1 is to be installed

Now I can't remove/install/downgrade to this version because apt would then remove about 200 packages including things like xorg, firefox, gnome-session and pretty much every package I ever heard of.

One other thing I wanted to try taken from the question here was

sudo dpkg --install --force all /var/cache/apt/archives/libpython3[version].deb

but there was no file with my needed version number.

Edit: I downloaded the specific version via apt download libpython3.6-stdlib=3.6.5-3 and installed it with above command. Now I can neither do upgrade nor autoremove, and I get this warning for both:

The following packages have unmet dependencies: libpython3.6-stdlib : Depends: libpython3.6-minimal (= 3.6.5-3) but 3.6.5-5~16.04.york1 is installed python3.6 : Depends: libpython3.6-stdlib (= 3.6.5-5~16.04.york1) but 3.6.5-3 is installed

What else can I do? Thanks for any help.