What worked for me was I installed and ran Thunderbird, then I quit and copied the Google Takeout .mbox file to ~/.thunderbird/xxxxxx.default-esr/Mail/Local Folders. When I re-launched Thunderbird, it took a few minutes and then all my Google Takeout emails were browsable/searchable under Local Folders.
Also, I think there was a weird step involved, like I needed Thunderbird to connect to some email account, any email account, in order to get past the welcome screen.
What worked for me was I installed and ran Thunderbird, then I quit and copied the Google Takeout .mbox file to ~/.thunderbird/xxxxxx.default-esr/Mail/Local Folders. When I re-launched Thunderbird, it took a few minutes and then all my Google Takeout emails were browsable/searchable under Local Folders.
Also, I think there was a weird step involved, like I needed Thunderbird to connect to some email account, any email account, in order to get past the welcome screen.