$ sudo chroot /mnt/linux /bin/bash
chroot: failed to run command '/bin/bash': Permission denied
The error is what it says: /mnt/linux/bin/bash was found, but you are not allowed to execute it, even if you are root.
You will get the same error message if you run the command directly:
bash: /mnt/linux/bin/bash: Permission denied
Most likely, the partition was mounted with the noexec flag, disallowing running any executable stored on that partition.
To check this, check the output of findmnt: