Numerous problems following upgrade to 22.04LTS

[mahesh]

Sorry this is such a long post. I'm not sure what is relevant and what isn't (or perhaps how many different problems I have).

My level of experience
More-or-less rank beginner. (e.g. I don't even know where to look for system logs etc if anyone needs information from them.) But I'm not afraid of the command line and if someone holds my hand for a while I can probably start to work out some of the simpler things for myself. Anything complicated will need spelling out, preferably in words of one syllable.

Where it all started
A couple of months ago I upgraded from 20.04 to 22.04; didn't really intend to but clicked the wrong button in a dialogue at the end of a long day so decided to let it run. 20.04 was itself an upgrade from 18.04 pre-installed when PC delivered late 2019 and had given no problems (original installation and 20.04 used Budgie desktop which was dropped for 22.04).

None of the subsequent problems have been permanent showstoppers. Some have taken considerable time to sort out; these all recur, seemingly randomly. Some have never been sorted but not necessary for my work so I've left them.

Problems
In no particular order:
Sometimes machine fails to boot, requests boot media be inserted. This has so far been overcome by changing boot order, sometimes several times; each of the available options has been used and all have worked at various times (I'll post details of the options I have if requested, if you know a way of finding them without rebooting the machine please say so).

If the system is left running overnight with several pieces of software open, one (Evolution email program) will usually have closed itself by the morning. When this happens, attempting to open one of the others (usually Firefox or LibreOffice Writer) results in that, too, shutting down. Attempting to open anything at that point results in a hamster wheel that runs for a while, but nothing opens; only solution is to reboot the machine.

Some of the programs listed in the 'Activities' option don't open at all; a particular example is Drawing. Some work for the most part but occasionally fail (one such is pCloud). Some I could open now fail (Synaptic is one, I seem to recall Drawing is also in that category).

Software installer seems to misbehave: I was able to use it to install software but it won't list installed software and when I try to check updates I get this error
Unable to download updates: E:http://dl.bintray.com/aluxian/deb stable InRelease is not (yet) available (Connection failed [IP: 3.121.3.67 80])

Shutdown or reboot is hit or miss. Sometimes behaves perfectly. Sometimes goes to black screen which then fills with message below (sometimes via the shutdown dialogue and sometimes not) -
[ ] systemd-journald[477]. Failed to write entry (yy items, zzz bytes), ignoring: Read-only file system.
This will occasionally finish in a reasonable time, other times it will run as long as I let it (but usually comes to an end and machine shuts down if left overnight). I have found various references to similar messages here, for 18.04 or earlier and with suggestions that don't seem to work when I try them - commands don't seem to be recognised by the terminal (unless I'm trying to input them in the wrong place - definite possibility, see above re my level of knowledge).

Occasionally while shutting down the system will pause, sometimes for rather a long time, showing the message -
Unattended-upgrade in progress during shutdown, please don't turn off the computer
Again this may sometimes be very quick or sometimes needs leaving to finish overnight. I wouldn't include it, except that there have been times when the Software Updater has failed, referencing 'unattended-upgr'. That now seems to have ceased, but the Software Updater now fails to download repository information. (Settings are default.)

Today I had the machine drop out to a black screen without trying to reboot, with the following series of messages appearing -
[ ] FAT-fs (nvme0n1p2): unable to read boot sector to mark fs as dirty
[ ] EXT4-fs error(device dm-1):_ _ ext4-find.entry:1612: inode #5513292: comm snapd: reading directory 1 block 0
[ ] Buffer I/O error on dev dm-1 logical block 0, lost sync page write
[ ] EXT4-fs (dm-1) I/O error while writing superblock
The last 3 lines were repeated after a while and it looked as if that would continue, but I needed the machine for the afternoon's work so forced a power-down.

Whenever the black screen appears, I have found that forcing a power-down resolves things (sometimes via the boot media request etc when I switch on again) so I can continue working.

Apologies again for such a long post, I have no idea what is strictly relevant and what isn't so please help me to narrow it down. Also please be aware I use the computer for my work and have a very full schedule, with several 12 hour days each week, so it may be some time before I can respond to requests or suggestions.

Any assistance would be most welcome.