Sony's using third-party manufacturers to produce its phones isn't unheard of. The Japanese OEM has been doing so with its mid-rangers for a while, but according to the latest report, Sony will likely outsource its high-end smartphone manufacturing as well.
According to a Japanese news outlet, this isn't temporary and is likely a long-term strategy. In fact, you can no longer find "smartphones" on the list of devices at Sony's own production sites in Thailand. Historically, three manufacturing sites were involved in Sony's smartphone production - two in Thailand and one in China. None of them lists "smartphones" anymore.
Sony Xperia 1 VII 5G
The report also suggests that the recently released Xperia 1 VII is the first phone to be assembled by a third party maker. For what it's worth we didn't notice any changes in the build quality when reviewing it.
Source (in Japanese)