I don't know the flatpak error you get, but spotify runs much quicker with their PPA/.deb without running in sandbox;
curl -sS https://download.spotify.com/debian/pubkey_0D811D58.gpg | sudo apt-key add -
echo "deb http://repository.spotify.com stable non-free" | sudo tee /etc/apt/sources.list.d/spotify.list
sudo apt-get update && sudo apt-get install spotify-client
I know I can install as Terminal, but I can't either update from software too
What does it say;
sudo apt update
It's Norwegian but I can translate for you
1 pakke kan oppgraderes. Kjør 'apt list --upgradable' for å se den.
1 package can upgrade, run 'apt list --upgradeable' to see it.
I understand what it says, I'm from Denmark 
Next;
sudo apt upgrade
Ah. So I run the command, and I was still trying to update on software and it still the same happend.
Can't upgrade org.freedesktop.Platform.ffmpeg-full: Can't create temporary directory
It's like 9 update list on software
Let's try with flatpak as the error is flatpak;
flatpak update
flatpak upgrade
This is happend when I type flatpak update
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Error: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Error: Can't create temporary directory
Changes complete.
error: There were one or more errors
And that happend when I'm type flatpak upgrade
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Error: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Warning: Can't create temporary directory
Warning: Failed to create a mountpoint for revokefs-fuse: Can't create temporary directory
Error: Can't create temporary directory
Changes complete.
error: There were one or more errors
And when I'm meaning type I meant copy/paste
See if this will do the trick;
flatpack repair
That command dosen't even exist
Sorry, it should be:
flatpak repair
a typo.
Oh gosh, that will take a while. I'll reply when It finishing
Take your time, i'll be offline for a while.
So It stopped on 86/174
I'm wondering if your /home is full. Can you check how much space you have left. Flatpaks/snaps is enormous in size compared with normal package and you got a lot of flatpaks installed.
The error complains about an app called; revokefs-fuse
Try uninstall that app;
flatpak uninstall revokefs-fuse
Sorry for late repsond. I copy/paste that command and gave me this
error: revokefs-fuse/unspecified/unspecified not installed
And I check how much space I have left, and I have alot of disk space. 8,4% full
Did some search on the net, not sure if this will work
The problem occurs due to incorrectly set permissions on the / var / tmp / directory , which flatpak actively uses . Solution:
sudo chmod 1777 /var/tmp/
Thus, writing, reading and executing become available to all users, while using sticky-bit - the user can delete only those files that he owns.
Checking the applied rights:
ln -ld /var/tmp/
Command output:
drwxrwxrwt 13 root root
The t at the end indicates the presence of a sticky-bit.
Note: In this example, the number 13 means the number of hard links , it may differ from distribution to distribution, this is normal.
The flatpak programs will now work correctly.
I do not know what is causing the Flatpak error, but if it was me, I would remvoe Flatpak.
flatpak list
Then use flatpak remove command to remove any flatpaks. You can replace what was installed as flatpaks with .deb packages for better stability.
Or, you can then reinstall flatpak as a fresh start:
sudo apt install flatpak
Then try only installing the flatpaks that you actually need and see if that halts the errant behavior.
That command gave me output error
ln: invalid option -- 'l'
Try to type "ln --help" for more information