@KatrinLeinweber Try setting options(pkgType = "binary") before running update.packages(). To make this always be the default behavior, you can add that line to your .Rprofile file.
Here is the relevant section from ?options:
pkgType:
The default type of packages to be downloaded and installed – see install.packages. Possible values are platform dependently
on Windows
"win.binary", "source" and "both" (the default).
on unix-alikes
"source" (the default except under a CRAN macOS build), "mac.binary.el-capitan" and "both" (the default for CRAN macOS builds). ("mac.binary.mavericks", "mac.binary.leopard", "mac.binary.universal" are no longer in use.)
Value "binary" is a synonym for the native binary type (if there is one); "both" is used by install.packages to choose between source and binary installs.