The issue you're experiencing is because recent versions of bslib handle Node dependencies differently. Instead of looking for node_modules directly, you can try this approach:

# Get the bslib installation path
bslib_path <- system.file(package = "bslib")

# Check for the actual Bootstrap files
bootstrap_path <- file.path(bslib_path, "lib", "bs")

# If you need specific Bootstrap files, you can look here:
bs_files <- list.files(bootstrap_path, recursive = TRUE)

The Bootstrap files are now typically located in the lib/bs directory within the package installation path. If you're trying to access specific Bootstrap components, you might want to use bslib's built-in functions instead of accessing the files directly:

library(bslib)

# Use bs_theme() to customize Bootstrap
my_theme <- bs_theme(version = 5)  # or whichever version you need

What specific Bootstrap components are you trying to access? This might help me provide a more targeted solution.