Where does Google Chrome automatically save pages?
This would be in Chrome data, which means you need root and on my device running 8.1 stock this seems to be it

/data/data/com.android.chrome/app_chrome/Default/Offline Pages/archives/ where you have .db (databases)

In one of the databases prefech_store, I could see the information pertaining to off-line pages

This may not help you as HTML/MHTML pages are not available directly for your purpose (searching for those in the app data didn't turn up any which implies they are stored in databases only)