European auto sector didn't loose because they didn't flood the country with enough low wage workers (which they did anyway since 2015) to compete with China on labor costs. They lost precisely because they gave up investing in local labor that made all the pricy high-end innovations like electronic brakes, self-driving and EV-tech, and entered in the race to the bottom to boost shareholder value while cutting the expensive innovation R&D. This strategy did wonders for EU auto shareholders for about ~10 years while the badge prestige carried a lot of inertia, especially in markets like Russia, US and China, but it lost most momentum in the last couple of years, as EU cars are now seen as dated, overpriced, cheaply made, expensive to fix and underwhelming compared to the new players from US and China. Nothing to do with lack of cheap immigrant labor.

US was investing in AI powered self-driving tech, China was investing in new EV motor and battery tech with advanced manufacturing automation to cut costs, EU makers were just reselling diesel engines with fancy badges hoping the EV and self-driving fad will pass. EU car industry went from decades of being the global trend setter in terms of designs and technology, to being the follower, at least in technology.

Also, a lot of the manufacturing costs in EU not just for the auto sector, is now majority made of taxes, compliance, bureaucracy and labor's cost of housing. If you import workers they'll be under the same high compliance rules, and same expensive housing pressures, unless you bet they'll accept to live in slum-like conditions in order to undercut the locals, in which case you might as well cut the facade and just advocate for return to slavery.