AIBU to be less than honest about my Airbnb stay?

A review should be accurate and honest, otherwise it's pointless.

The point of leaving a review is to help inform future guests. There's absolutely no reason to mention next doors building work in this review as it's almost complete so won't impact anyone else booking.

Fine to mention the unkempt garden though.

My family say that I am very noise sensitive - which is true

I think if you know that about yourself, you need to message the hosts, like you’ve said. Reviews aren’t going to be accurate enough for you because it seems you’d be affected by noise that wouldn’t bother most people.

I wouldn’t mention the construction noise as you didn’t contact her, and so she had no chance to do anything, plus it wasn’t directly her fault. I’d mention anything else that felt fair but you’ll need to assess how much the other bits would have bothered you if you weren’t already on edge from the increased noise.

Did the host warn you far enough in advance about the building work that you could have still cancelled without payment, and was the quietness a key advertised feature of the property? That would be important for me in determining whether to mention it in a review.
I‘m like you in being really positive generally about reviews, but on occasion with small things I‘ve not mentioned them in a review and given 5 stars but then told the host in a private comment. An example of that was a fairly basic property in the mountains (priced fairly as such) where the cleaner had generally done a good job but completely overlooked the shower door joint when it was fully closed - when open the dirt was hidden, when having a shower you could see the filth. It was clearly an oversight because the cleaner never personally showered there - I just let the host know to pass it on for future stays.
For another stay the bedroom loft was accessed via very steep stairs and I did say in the review that it was great for us but not suitable for anyone with mobility issues - a fair and true comment which wasn‘t immediately apparent from the pictures.
In your case the building work will soon be over so no point warning future guests. The damp smell is minor enough for me to mention in a private comment to the host. But I would mention in a review if the pictures of the garden were erroneous.

So I tend not to mention in reviews what falls outside the host’s control.
But of course it's in her control. She chooses who she lets to and when. She could just not let it out if she knew it would deliver a suboptimal experience to guests (and maybe spend that time when it's not being let actually sorting the garden out). The fact that she doesn't just stop letting it until she can provide a decent experience says she cares more about the money than the guests.

I'm sure someone will be on to say blah blah whatabout mortgage blah but honest to God if you can't afford your second home Air BNB isn't there to prop your failed business up. Guests should always come first.

I would definitely not mention the building work in a review. The other aspects are reasonable to mention if you felt inclined.

Also - the host warned us that there would be building work at the neighbours property but it was nearly done and to let her know if it was a problem.

The host warned you and said to let her know if it was a problem so you would be unreasonable to write about it in a review if you didn’t contact her during your stay to say it was an issue

Im in a somewhat similar situation. Just returned from a holiday in Spain. Spent second part of it in on the north coast in Asturias and rented an Airbnb chosen as it was a guest favourite, within our price range (it’s quite pricey there in august) and town it was in looked pretty based on some online research. The place had glowing reviews and while it was all fine and hosts very communicative it was overall underwhelming and I can’t work out why the reviews were so glowing. Part of my issue with the place (that it was on a rather unattractive street with no good views) seems a bit unfair to reference in the review as I could have worked it out if I’d done more research beforehand, but in addition the place could have been cleaner, the kitchen was cramped and not that well equipped and the tv was v old with no smart tv services. I have not reviewed it yet . . .

I don't think it's fair to mention the building work when it's nearly done, the host warned you, and they said to let you know if it was an issue and you didn't.

Can you message the owner first, just in case they don't actually know about the problems (other than the builders)? Then, you can say you had a couple of issues but the owner is sorting them for future guests. Win, win. You're not lying by hiding it, but you are also not landing the owner with a problem they maybe aren't fully on top of.

I would review honestly. I've been caught out before with properties which have good reviews and then when we arrive there are lots of problems. I'd rather people told it like it is.

I think it’s wrong NOT to review honestly as others are relying on your views and opinions to help them make their choices . I’m never disingenuous in reviews .

She could have spoken to them I guess. If she asked you to let know, and you didn’t, I do think it’s a bit off then complaining in the review. As you say, host had no choice and it you stay in these types of lets, you have to accept that real life goes on around it, such as work on neighbouring properties.