I can't load packages in R because the file libpq.5.dylib is not in /usr/lib/libpq.5.dylib. It is in /usr/local/Cellar/libpq/13.0/lib/libpq.5.dylib
I tried this line: sudo ln -s /usr/local/Cellar/libpq/13.0/lib/libpq.5.dylib /usr/lib/libpq.5.dylib but I get this response: ln: /usr/lib/libpq.5.dylib: Operation not permitted
What can I do to get the file in /usr/lib/libpq.5.dylib without causing issues? This solution suggests that I may face problems down the line so I don't understand what to do.
You really don't want it in /usr/lib. Apple declared that as off-limits, and on newer macOS versions it lives on a read-only volume. Unless you're willing to go into recovery mode and manually tamper with the volume (and possibly repeat that on future OS updates), this is not the way to go.
Instead, let's address the core issue:
Dynamic libraries on macOS embed their own install path inside the binary, and the linker copies that into binaries linking against them. This information can be changed with install_name_tool (see man install_name_tool).
Examine the install name of the dylib:
otool -l /usr/local/Cellar/libpq/13.0/lib/libpq.5.dylib | fgrep -A2 LC_ID_DYLIB
If the printed path already points to the dylib itself (or a path that is symlinked to it), use this path as [new_path] below, and skip step 2.
If the dylib's install name does not point back to itself, run this:
sudo install_name_tool -id /usr/local/Cellar/libpq/13.0/lib/libpq.5.dylib /usr/local/Cellar/libpq/13.0/lib/libpq.5.dylib
And use /usr/local/Cellar/libpq/13.0/lib/libpq.5.dylib for [new_path] below.
For binaries that link against the dylib, run:
sudo install_name_tool -change /usr/lib/libpq.5.dylib [new_path] [path_to_binary]