I was reading an article about this, it started before trump got into office and sounds like it stems from a complaint from a solar panel manufacturer in Arizona who claimed they could not make theirs as cheaply as these countries could. Whether or not the size of the tariffs have anything to do with trump I have no idea. Although it should be noted one of the manufacturers has only a 40% tariff, another is something like 232%.

Edit to add a link to a source https://www.theguardian.com/business/2025/apr/22/us-huge-tariffs-south-east-asian-solar-panels-energy-summit