You probably need to pass the iocharset mount option.

#!/bin/bash

#
***
Configuration
***
SOURCE_DEV="/dev/sr0"
MOUNT_POINT="/mnt/mac_legacy_cd"
DEST_DIR="$HOME/Desktop/mac_recovered_files"

# 1. Ensure the system is ready
echo "Checking for HFS support..."
sudo modprobe hfs 2>/dev/null
sudo modprobe hfsplus 2>/dev/null

# Create directories
sudo mkdir -p "$MOUNT_POINT"
mkdir -p "$DEST_DIR"

# 2. Attempt to mount
# We try HFS first with MacRoman to UTF-8 translation
echo "Attempting to mount $SOURCE_DEV..."
sudo mount -t hfs -o ro,iocharset=utf8 "$SOURCE_DEV" "$MOUNT_POINT" 2>/dev/null

if [ $? -ne 0 ]; then
    echo "HFS mount failed, trying HFS+ (Mac OS Extended)..."
    sudo mount -t hfsplus -o ro "$SOURCE_DEV" "$MOUNT_POINT"
fi

# 3. Verify mount and Copy
if mountpoint -q "$MOUNT_POINT"; then
    echo "Mount successful. Copying files to $DEST_DIR..."
    # -a: archive mode (preserves symlinks, permissions, times)
    # -v: verbose
    # -z: compress (not really needed for local, but good practice)
    # -P: show progress
    rsync -avzP "$MOUNT_POINT/" "$DEST_DIR/"
    
    echo "---"
    echo "Copy complete. Unmounting..."
    sudo umount "$MOUNT_POINT"
    echo "Done. You can find your files in $DEST_DIR"
else
    echo "Error: Could not mount the disc. Ensure the CD is inserted and $SOURCE_DEV is the correct path."
    exit 1
fi

Not sure what the actual question is here, but if the files are there, the filesystem is mounted properly using hfsplus, and you can read the files, then any incompatible characters will be properly substituted, and the files can be copied.

Your friend will just have to put some work into properly renaming then afterward.

I haven't needed to do this myself but have a few ideas if you haven't already tried these yet

• Are you trying to mount as HFS, or as iso9660? Those CD media you are looking are are probably hybrid ISO/HFS discs so they technically can be read in either format.. I suspect mounting as iso9660 with/without its mount options could help you copy the data afterwards. Check the man page for mount to review the options, thinking iocharset and/or utf8 could be helpful if the defaults aren't working.

• If the standard mount / cp isn't working you could also give other tools a look. Have not tested this myself but I saw the Debian repo has hfsplus - which includes hpmount and hpcopy which should in theory be able to copy off HFS+ media. No idea if the tool also works with HFS but could be worth a go.

If nobody has a better idea, you could create a loop device with a HFS filesystem, copy the CD to that filesystem, replace all bad filenames, then copy everything to a normal filesystem.

Edit: apparently there's a --iconv option in rsync: https://askubuntu.com/a/540960

Spin up a hackintosh to read it.

Have you tried creating a period-accurate Mac VM, allowing passthrough of the drive peripheral to the VM, then copying the data from the VM to something like a Mac format flashdrive?