The Germanic origins of the Franks were well known to have reemerged in French historiography, which in the XVIIIth century, after a long period where the origins of the French nation did not oppose nobility and the general population extensively described a fabled distinction between a Germanic descent noble class and Gallo-roman peasants, which bears very limited historical truth (the Franks heavily relied on late Roman authorities to settle their rule, and did not reach over the southern part of the country). Michel Foucault, in his conference cycle of 1975-1976 called Il faut défendre la société extensively discusses this historical myth and its invention in the XVIIIth century (https://monoskop.org/images/9/99/Foucault_Michel_Il_faut_defendre_la_societe.pdf, p. 87 sqq) :

Si, en Angleterre, la conquête et la dualité raciale Normands/Saxons étaient le point d’articulation essentiel de l’histoire, en France en revanche, jusqu’à la fin du XVIIE siècle, il n’y a aucune hétérogénéité dans le corps de la nation, et tout le système de parenté fabuleuse entre Gaulois et Troyens, puis entre Gaulois et Germains, puis entre Gaulois et Romains, etc., permet d’assurer une continuité dans la transmission du pouvoir et une homogénéité sans problème dans le corps de la nation. Or, c’est justement cette homogénéité qui va être cassée à la fin du XVIIE siècle, et non par un édifice théorique, ou théorico-mythologique, supplémentaire ou différent, dont je viens de vous parler, mais par un discours qui est, je crois, de type absolument nouveau par ses fonctions, ses objets, ses conséquences.

"While in England, the conquest and the racial duality between Normands and Saxons was the core articulation of historiography, in France, until the late XVIIth century, there was no heterogeneity in the national body, and the entire system of mythological origins linking Gauls and Trojans, Gauls and Germans or Gauls and Romans allowed safe transmission of power and national homogeneity. And it is precisely this homogeneity that came broken in the late XVIIth century, not out of an additional or different theoretical or mythologico-theoretical apparatus, but through a discourse that was radically new in its functions, objects and consequences".

He later analyses that the emergence of these theories, linking nobility and a different race (biologically speaking, or at least genealogically speaking) in the second half of the XVIIIth century as the reaction of the French nobility versus the constitution of an administrative apparatus in Versailles, to reassert their singularity in the national body through biopouvoir mechanisms (in typical foucaldian fashion).

As indicated here, in any case, those theories were just theories, reemerging after centuries of no distinction between "invaders" and "invadees".

Earlier, there were still traces of a nuance between Frankish invaders and the local population possibly as late as the VIIth century (Gabriel Fournier, Les Mérovingiens, Presses universitaires de France, collection Que sais-je ?, juin 1987) with complete disparition of any ethnic perceptible distinction through intermarriage between the Gallo-roman elite and the Frankish ruling class.