I've had to look this up because everyone also brings up this point without any proper details.
The exact numbers are not known. It's supposedly 45%-55% (at the beginning people were claiming 70%). It's limited to 2 factories. One in Odessa and one in Mariupol.
Both of them shut down somewhere at the start of this whole endeavour. The Mariupol one is already in the hands of Russians. It wasn't that close to Azovstal, so it's due to reopen. The one in Odessa will not reopen until the Russians either take it or Ukraine agrees to the deal judging by all the missile strikes. But for the short term future its out of commission.
The fundamental part here is this:
If this is really such a big deal as everyone claims it is, then people will inevitably have to find a compromise with Russia.
But I will repeat again one thing that people don't seem to grasp. Arounds 30% of the worlds commodities are exported by Russia, another ~30% are exported by the US. The difference between these two is that Russia exports its own commodities and the US exports not only its own, but also its "little colonies" like Trinidad and Tobago commodities. You cannot just turn off the tap on 30% of the worlds commodities.