>>514867337 (OP)
High IQ, high conscientiousness, high orderliness, disease-free women under BMI 24 and age 35 are pretty much always allowed to immigrate.
They are not allowed to pull in the rest of their families for long-term stay, but short-term visa is okay.
Thought experiment is "Germany with zero immigration" vs "Germany with 100,000 or more fertile healthy high IQ single women" and of course, the latter makes Germany much more successful and sustainable and only a tiny bit less German. Loss of German-ness through the many mixed HAPA babies is far lower than the loss of German-ness through the birth strike of native German women.
If all German women would have 4+ children with German men, then that would be the best way, but they don't and they won't. Their mental illness is terminal and will not be cured before their bodies will run out of follicles.
Half-German babies that are actually born are more German than full-German babies that are never born.