his sources are basically YouTube and other unproven articles, mostly from far right extremist sites.
German truth check article for that one: https://www.volksverpetzer.de/uncategorized/uni-hamburg-unwi...
Within one day of the press release this has drawn so much negative attention in Germany that this "study" became a major embarrassment for the university and its press department. Now they are mostly concerned with damage limitation...
Physicist professor.
Autotranslation:
https://translate.google.com/translate?hl=&sl=auto&tl=en&u=h...
> The study was carried out from January 2020 to December 2020. [...] It does not provide any highly scientific evidence, but does provide numerous and serious evidence:
Even the press release of the university acknowledges that It does not provide any highly scientific evidence.
> The study is published at: http://doi.org/10.13140/RG.2.2.31754.80323 .
Note that this is a link to a preprint in ResearchGate, not a peer review article. This has the same checks levels than a blog post in WordPress. It is "published" but essentially anyone can publish there whatever they want.