The underlying grievance is of course not over "increased diversity" per se but rather the long-term decline in civic attitudes. The progressive left expresses the exact same concerns in a different wording, by decrying the increased "marginalization and exclusion" that's seemingly entailed by such diversity. Guess what: they're all looking at pretty much the same thing.
I fail to see how the previous US president's complaints about people coming from "s*hole countries" and the exhortations from the Charlottesville rioters about how "Jews will not replace us" are grievances about "decline in civic attitudes". Try as one may to dissociate them, but these are the faces, words, and animating motivation of nationalism today.
Your argument is intentionally mixing "is" with "was".
Marx died 140 years ago, and there are no ethno-nationalist voices of significance on the left today. In the US context, after the civil rights movement of the 20th century those people left the Democratic party as the parties realigned themselves.
Today it is largely a right wing phenomenon, carrying forward the tradition of right wing ethno-nationalism that persisted from the previous century.
> It's barely right/left at all, it's just nihilistic power as its own end.
These statements are skillfully leaving out "ethno" part of nationalism. Once you add that quite obviously real and active element back, it's very much a left/right difference.
The left's solution to the problems brought about by globalization is to subtly bias the scales of re-industrialization policies toward the domestic labor market - evidenced by things like the battery materials sourcing and assembly location requirements, and income limits of the recently passed EV tax credits.
The right's solution to this has been playing on fears of a purported invasion by non-white citizens from lower income countries. A decade ago that would have been a controversial claim to make about the right, but today's right openly proclaims those ideas.
Portugal's case is interesting because they lived under a nationalist dictatorship that only ended in 1968, so many people alive today remember living under that. In my travel there, I found that many people in the age groups that vote heavily conservatively in the US and UK instead vote democratic left as a result of their lived memories of nationalist dictatorship.
Portugal does need to figure out what else has to offer the world economically in addition to great weather and beautiful cities and countryside, in order to have a better balance of trade, but it's unrealistic to think it can do that while shutting down immigration.