There are two problems with ethanol, one practical and one stupid.
The stupid problem is that it's taxed heavily and thus is stupidly expensive. When not taxed it is probably denatured, but denatured with what? If you know the denaturant then you can use it with some degree of confidence. Methanol (methylated spirits) is acceptable in almost any technical application but is somewhat toxic, so for stupid reasons it is now rare. Denatonium benzoate is the other common denaturant, but it can leave annoying residues behind. Pick your poison (literally).
At one point in my career we had ready access to untaxed, undenatured, 200-proof absolute ethanol. So I used it a lot! Turns out it's significantly more aggressive than isopropanol, and can strip coatings or generally even dissolve things that isopropanol cannot. I don't use ethanol any more, I have better things to do with my life than figure out what it is and isn't going to dissolve.
I use 99.9% ethanol for electronics cleaning (not very frequently) and it leaves a white residue on some PCBs (e.g. JLCPCB ones?), but not all. It also seems more aggressive if I accidentally get it on my skin. Doesn't smell as bad as IPA though!
I haven't heard that IPA is much worse than ethanol though, beyond what's stated on Wikipedia ("somewhat more toxic"; ethanol is obviously toxic as well). Should I be more concerned about using IPA?
Personally I am not really concerned about any toxicity differences between ethanol and isopropanol. As the sibling comment says, they're both widely used in hand sanitizer. At the exposure levels present in electronics work, and compared to the other stuff that's going to be around, it doesn't seem worth worrying about to me.
The white residue is a separate problem. Alcohols are not perfectly effective at dissolving all the components of flux residue, so you often get white crud left over. It's harmless, but ugly, and sometimes you just need a clean joint. I think it is possible to get this stuff off with alcohol and some skill, but who has time for that? Just buy proper flux remover.
The best flux remover I know of is MicroCare SuprClean or PowerClean (they're very closely related, but definitely at least a little different; either way it's hard to tell them apart, so go for whatever's convenient). It is supposedly nontoxic (but remember they once said that about the last flux remover that got banned... and the one before that... and...), readily available from the usual places here in the US, and very, very powerful. Careful cleaning with it will not leave any white residue behind. (Careless cleaning will lead to the observation that flux remover solvents dissolve soils... which means the soils are right there to be redeposited should the solvents evaporate... so you have to actually manage to get the crud off the board if you want it clean. Dissolving alone is not enough!)
I haven't done an exhaustive survey of flux removers, but this stuff certainly does the trick. I was originally looking for something that could dissolve Krytox residues (long story) and while I thankfully never had cause to test it, this stuff is based off some member of the Vertrel family, which is one of the few things in chemistry capable of that job. And anything that can even threaten Krytox is probably a tool worth having!
Not really. The entire planet was rubbing it on their hands for years during the pandemic. It'll dry your skin out, sure, if you're getting a lot of it on your skin, but you shouldn't be if you're not using it as hand sanitiser, and of course you're not drinking it.
Occasionally I will "wash" dirty PCBs by spraying them with 50% ethanol, 50% water, then drying them with an air gun or the like to get the water off in a reasonable time.
Nearly any properly designed board will not hold residual voltage for long when disconnected from power, so the slight conductivity of tap water is a non-issue.
The stupid problem is that it's taxed heavily and thus is stupidly expensive. When not taxed it is probably denatured, but denatured with what? If you know the denaturant then you can use it with some degree of confidence. Methanol (methylated spirits) is acceptable in almost any technical application but is somewhat toxic, so for stupid reasons it is now rare. Denatonium benzoate is the other common denaturant, but it can leave annoying residues behind. Pick your poison (literally).
At one point in my career we had ready access to untaxed, undenatured, 200-proof absolute ethanol. So I used it a lot! Turns out it's significantly more aggressive than isopropanol, and can strip coatings or generally even dissolve things that isopropanol cannot. I don't use ethanol any more, I have better things to do with my life than figure out what it is and isn't going to dissolve.