Sorry OP that this is where you find yourself.
Reading through your posts I wonder how well you are communicating to him what you want - and whether you actually know what you want yourself:
I have always said to him I would only want him to propose just to know he meant it/more romantic
I’ve never been desperate for marriage but always made it clear if he asked me I would say yes
I was never crazy for a wedding but I just assumed we would naturally have a low key one one day
The baby before proposal was simple really, he always knew when we would be TTC and it doesn’t happen overnight (not in our case certainly!) so every other month that went by I thought, ok, he’s cutting it a bit fine now but it will happen soon.
It sounds like marriage has been discussed, at best, as quite a nebulous "one day" thing that isn't hugely important to you. Then you agreed to TTC - did you not, at that point, have any further conversations about marriage? Like "yes we agreed we'd ttc at 35 but to be clear I want to be married before the baby is born?"
From your posts it sounds like not a lot of communicating is going on at all here, and you were silently hoping he'd have some epiphany whilst ttc that he "should" propose despite having not really talked about it, and now you're silently very upset that he hasn't.
As per PPs, I think you need to work out what it is you want. Because actually it sounds like you don't really have confidence in how he feels about you, that he does want to spend the rest of his life with you, which is why you've set this spontaneous romantic proposal as some sort of test to prove that he really does. When perhaps your gut is telling you something else. If that is the case, I'm afraid I don't think your gut instinct is going to change with a spontaneous proposal.
You need to do some long hard thinking here about what you really want here and why. Is it marriage (relatively easy to fix) or is it the spontaneous proposal (which realistically you probably won't get)? And if the latter is more important to you than the former, you really need to think about why that is.