As things stand now, maybe the EU will continue to do business with Russia when it comes to gas - if nothing has changed in such conditions (gas is still delivered), by next winter the whole situation will calm down, because this war can not last longer of several months. The EU has already opted for renewable energy sources in the long run, so that at some point in the relatively near future the whole gas and oil thing will be irrelevant.
Based on top-5 countries by
natural gas reserves, Iran is a good option, and the US has fair reserves itself.
Iran is still under sanctions (if nothing has changed), and is there any gas pipeline that would bring gas to the EU? And when you mention the US, in that case the EU would have to build a number of LNG terminals and pay a much higher price for gas, which is certainly one of the options, but I'm not sure what EU bureaucrats think about it.