We have one person who will put various things like this including 'lulz' 'broke shit'
Even more infuriating when their is no ticket number.

I'd bring that up with your boss, if they get hissy about things breaking and wanting fixes, tell them we need more QA time or a QA team. I agree automated testing will only get you so far and if you have no time for it then no time is spent looking at the testing to improve it. Things take time and if you're having to crank out dev work constantly with no time for process improvement, then things will break, or worse you'll burn out

They should just have the requirement of it needs save/save as. Let the UI/UX peeps deal with that

Is there no QA process at all?

At our place it's a case of
- reproduce on prod
- reproduce on staging
- push fix to staging and QA verify
- push to prod
- verify

That can catch the bugs but also detect repercussions elsewhere in the system

Amen.
The current reason why I'm feeling so fed up

Sadly murder is not an option. I have a similar issue, it's either very vocal/angry/shouty/toys out of pram or the same in messages. Some days it really makes me feel about changing job, but I'm on a good deal at my current employer

Can't you not just queue it? Or does completion take a successful request to their api

I suggest getting in touch with a mental health care specialist, also if you trust your boss let them know.
It could very well be depression or low mood. Until you discuss it you won't know what to do. I did CBT and that sort of helped. Little things like going for a walk, exercising, reading a book before bed, sharing my thoughts and feelings helps me.

Some days I get told I'm doing a good job or overworked, but currently I feel I'm just bored, slacking and fed up, but that's a reflection of my own mental health

I generally do. Ours cover multiple products and do support.
I kind of feel sorry for them. Us devs have no time for tests so you poor sucker's got to check it (we got to check it first) I wish some of the stuff they do can be automated but no time for that. But a lot of time they find inconsistencies and how somewhere way far in the edge of the system is affected by the change, but we iterate so fast automated sections so fast, automated testing would be pointless
Also steps to reproduce, screenshots, console errors/network are handy

You sound local to me. I'm in Portsmouth!