How Do I Fix Photo Dates on Ubuntu?
You can do it with exiftool at the terminal, or with an app that reads your Takeout files and writes the dates in for you.
The command line route is exiftool, which is in the Ubuntu archive. It is powerful and it is exact, but you have to write the command that matches your particular mess, and a wrong one is hard to undo.
The other route is an app that already knows the shape of a Google Takeout export: which .json belongs to which photo, what Google's odd filenames mean, and which date to trust when they disagree.
Takeout JSON Metadata Fixer ships as a .deb and an .rpm and runs on the desktop. It runs on your own computer and is free for your first 500 photos.