enc2utf8 issue with render_book() from bookdown

Do you have an example you're able to share ?
It would be easier to investigate.

Do you know which version of packages worked with your old book ? You could try installing previous versions of the package if one them may have cause you breaking change.

For such project in the future, you should considered to lock your environment so that changes in package Versions are controlled and you can easily reproduce in time. Look at renv for that