I used the Iron Age Thracian versus Mordovians to calculate the genetic makeup of the Serbians. I got 51% Mordovian and 49% Thracian, which is is not far away from, ironically, 49% Mordovian and 51% late antiquity Roman native of Serbia, the result we see in the study.
However when using Czech Avar Slavic sample you get 65% Slavic and 35% Thracian, so probably roughly 60%/40% for the Roman Period.
This Slavic sample carriers Germanic admixture, which was not widely spread in late antiquity Roman Serbia as seen in the study. So a 60% contribution from Slavs and Goths combined together seems to be the accurate percentage.
I think it's better to investigate the Germanic admixture in Tuscany and some regions in Italy (expect for some northern regions like the case of Lombardy that has significantly more Germanic input than any region of the Balkans). Because I think the Germanic input in most Balkans will be lower than the Germanic input in Tuscany, so that we might know the "maximum". Which is a helping puzzle.
You can take a look at Maciamo's map of Germanic dna in Italy, which shows 5-10% for Toscana, and he provides the citations for the papers he used.
I'm aware there's a map floating around the internet by someone named Passa, whoever he is, and it shows about 10-12%. However, I've never seen a list of the sources so that his figures can be checked.
Given my knowledge of the castles established by the Langobards, and the relative paucity of the actual Langobards manning them once you leave the Veneto, I would think around 7% for Toscana would probably be the highest level, for the province as a whole, although that's a guess.
Given that Toscana plots west of Albania, I would think Germanic dna would only be a few percent in Albania.
We would need a lot more samples for anything approaching accuracy.
Fwiw, I have seen the results of a few 100% Tuscans, and total steppe is around 25-30%, depending on the area, with the northern areas having more. However, imo, the vast majority is "original" steppe admixed/Italic, Celtic/Gallic, and then a bit of Germanic; the latter is much less common in Toscana than in northern Italy
The following may be informed by my own subjective biases, as these kinds of statements often are, but while there is a great deal of phenotypic diversity in Italy, with some Northerners overlapping with those in other countries, and the same for Southerners, Tuscans, to me, often look "Italian", and "only" Italian. Note all the qualifiers.
(Sorry I didn't respond to you directly. The site is slow and kept blocking the response even though I removed the picture.)