The effectiveness or not of sanctions is an often debated point. For example, I was reading up on the actual impact in one of the "success stories", South Africa de-Apartheiding in 1994. Even there the story isn't crystal clear and it took years in any case.
Yes, there is possibly a bit of theater going on: "we're doing something, honest".
However, if we assume that the West has a vested interest, for whatever reason, in stopping Russia from taking over Ukraine, sanctions are one of the few possible levers and far from the worse.
Unlike lots of past sanction regimes these sanctions are brutal, were imposed very quickly and have a very wide array of participants, some of whom, like Switzerland, probably figured in the list of sanction-mitigating assets Russia could count on. Ditto the central bank's hoard of foreign currency being put offline for now.
These are sanctions, they take a long time. Expecting them to move Putin out right now is unrealistic. But I expect they will weigh heavily on Russia's future decisions and their imposition is also a message China can't ignore, after decades of fairly toothless Western sanctions in other cases.
The long term outlook for gas/oil is in a way even worse - with global warming very much on the mind of European electorates, any gas and oil Russia does not sell now they may not be able to sell later on if the sanctions run some years.
This is being done. And it is not without escalation risk - the US took great steps to be "plausibly deniable" in Afghanistan in the 80's - this was bypassed this time.
Because Russia is nuclear-armed this is a non-starter unless Russia attacks NATO first.
"Strong UN measures".
Russia has a Veto. So, no, not going to happen.
This is being done and make no mistake, they are pretty darn strong sanctions. Personally, I don't remember anything as ferocious and quick to be placed as sanctions in decades of following international news.
The Russian-on-the-street, whatever their government is telling them, is also being, very quickly, notified that the "special military operation" is generating a lot of push back. Not least because independent profit-seeking entities like Apple or Starbucks also jumped ship. When even "soulless beings" like an oil major (BP) are bailing, you know there's widespread revulsion.
Body bags will come, but the Kremlin has experience in suppressing their public awareness and sanctions beat them at the ethical level (Russian conscripts getting killed may be a military necessity but hardly cause of celebration).
There is also a misunderstanding how sanctions work. They are never waterproof, they inflict costs. Say you sell $100 of oil that normally cost you $60 to produce -> $40 profits. Given sanctions and time to evade them you might sell that oil at $90 (the buyer is going to ask for a discount and you have bribes to pay). But then your production inputs may also have jumped up to $70. $20 profits now, not $40.
So the West is using both of their realistic options, sanctions and military aid. The only other option is really to do nothing.
In fact the sanctions are so punitive that some say that they need to come with a clear indication of what would cause their withdrawal otherwise Russia may perceive no choice but to double down.