TLDR Poland from 1st to 5th century was settled by goths. Poles from middle ages were Slavs who mixed with local goth women. Very recently a demographic boom closer to Ukrainian border caused shift, but still, every 10th Pole descends from goths.
>Dr. Łukasz Łapiński - historian, genealogist who understands the meanders and methods of genetic genealogy, popularizer of archaeogenetics in Poland - summed up the publication of Prof.'s team on Facebook this way. Figlerowicz: "We will have to wait for the results of the Piast DNA, but in the meantime groundbreaking data has been published regarding archaeological DNA data from the Roman period and the Middle Ages in Polish lands. (Middle Ages - mainly Greater Poland). The theory of autochthonous Slavs from the Vistula River finally collapsed, but at the same time we said goodbye to the theory of the "settler void" from the period of the late Roman Empire. DNA clearly shows that the population of Polish lands from the Iron Age was significantly different from the population that has lived here for the last 1,500 years. However, according to research, a large part of women from ancient cultures remained here, who are our great-great-great-great-grandmothers, as well as a certain part of the old Gothic-Vandal (?) population. On average, every 10th inhabitant of Poland may be a descendant of ancient peoples from the Iron or Bronze Age (Celts? Goths? Lusatians?), meanwhile most of us are the result of the demographic boom in the territory of the Polish-Slovak-Ukrainian border (originally mainly Ukrainian), which occurred in the turn of our era. In a few years, computer algorithms will probably be able to determine it more precisely.

https://eurogenes.blogspot.com/2023/11/wielbark-goths-were-overwhelmingly-of.html?m=1
https://tygodnik.tvp.pl/71930106/nasze-matki-pochodza-z-kultur-starszych-niz-rody-ojcow-jak-gotki-slowian-pokochaly