Sorry, but as if. Russia is a UN veto power. And Russia would never accept UN troops sent by the West to oversee anything. And african nations won't want to piss off Putin by agreeing to this. Putin wants his anti-NATO back and this war will only end with Putin thuroughly defeated.
Not to mention that such a vote would be a farce anyway. Russia has had enough time to kill, torture, intimidate or disappear enough people that such a vote could never be fair.
And as for the money spent on Ukraine, it's but a cheap talking point to suggest that supporting Ukraine and supporting your own population are mutually exclusive. Not to mention believing that if the money wouldn't have been spent on Ukraine, that your own people would've seen that money is pretty delusional. For starters, most of the support sent by the US is hardware. And the given value for that support is the replacement cost for the kit sent. However, most of the kit sent was due to be replaced anyways, so the actual cost for the US is much lower than the figure being thrown around.

Negotiate an end to the war.

Russia refuses to give back the lands seized.

Now what to you do?

I’d support a UN monitored vote in the Donbass region and Crimea (and any other contested area) on whether they want to join Russia or stay with Ukraine.

Not an option the Ukrainian gov will accept. Nor should they.
When parts of the USA wanted to leave that was not response from the USA.