Most horrifying is a 2014 Science paper on Ebola with 58 authors, 5 of whom died of Ebola before publication. https://www.science.org/content/article/ebolas-heavy-toll-st...

The ATLAS-CMS joint Higgs boson mass measurement paper has close to 6000 authors: https://doi.org/10.1103/PhysRevLett.114.191803

I think the final COVID consortium report has something like 30k authors.