Recently one Serb from Eastern Serbia was confirmed at YSEQ as E-L540>A6295*, TMRCA 1500 ybp, in cluster with some Poles and one "German/Swedish" clade. Lusatian Sorbs have been tested in two studies (Population study and evaluation of 20 Y-chromosome STR loci in Germans; Contemporary paternal genetic landscape of Polish and German populations) with samples of 29 and 123 respectively, in both of these a E-L540 haplotype unified by dys448=21 can be seen, together from both studies haplotype is 25/27 with the E-Y153993 sharing 448=21, and other STR's indicate clearly Sorbs are E-Y153993. This German (I don't know surname) at YFull is either a Sorb or has recent Sorb ancestry (he's from the province where that ancestry is common).

So this Serb is only 1500 ybp distant from Sorbs. Some Serbs are R-Y2905, potentially also linked with Sorb cluster. But among Sorbs for example very common in Serbs I-PH908 is 0/152, though 4 I2a Din that are non PH908 are found (most likely unrelated to Serbs). So interestingly there is a genetic link between Serbs and Sorbs through one E-V13 subclade, and not through I2a Din.
Ofc this is a clade under E-L540 which is a basal Central/East/North Euro clade but still..

I've seen views explaining these weak Serb-Sorb links that Lusatian Sorbs are not real Serbs but they only entered Serbian tribal alliance and took the name. That the descendants of real PH908 Serbs were more to the South (Western Czech rep) where some PH908 diversity is found (Nabian Serbs/Nabsky Srbove/Chodové). Anyway there are few Lusatian Sorb traces found that at least date from that alliance and this V13 clade seems to be one pretty certain link.