When I went from Windows 7 to Windows 10, I thought I copied my profile folder from one computer to the other and then edited the profile.ini folder to use my old profile. That apparently doesn't work anymore.

Essentially that is so.

So, I uninstalled Thunderbird and restarted my computer. Reinstalled Thunderbird thinking I would have a fresh install. No, my old profile and edited profile.ini file are still there. How do I get rid of the changes that I made and transfer Thunderbird the correct way? TIA

Close Thunderbird go to the windows file manger and type %appdata% into the location bar and press enter. delete the Thunderbird folder and it's sub folders as that is the default profile location and certainly where you profiles.ini is located. Restart Thunderbird.

Now if you have difficulties with import (my profile is simply way to ig.) whomever thought such a small zip would be adequate I do not know. Additionally the "correct" import looses your passwords (yay!)

So in whatever profile you have in Thunderbird, go to the troubleshooting information on the help menu and click on the show profile button. (Sure you go to somewhere in %appdata% but this way you locate exactly where Thunderbird thinks the profile is.

Close Thunderbird. Paste/Copy you import profile into the folder replacing what is there. Restart Thunderbird. It should just work.

What you advised is essentially what this tutorial says https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

It still doesn't work. I wonder if there isn't a problem with my .ini file

[Install8216C80C92C4E828] Default=Profiles/yey54dn6.default Locked=1

[Profile0] Name=tendo IsRelative=1 Path=Profiles/yey54dn6.default Default=1

[General] StartWithLastProfile=1 Version=2

Any ideas?

The yey54dn6.default is my profile from my old computer

This is the error message that I get when I follow the instructions in the video https://support.mozilla.org/en-US/kb/unable-launch-older-version-profile

I started Thunderbird with the profile manager. If I mouse over the profile that is listed, it shows the correct path to the profile I mentioned users/tendo/appdata/roamig/thunderbird/profiles/yey54dn6.default

If I choose that profile and start Thunderbird, I of course get the above error message. I am desperate here. I don't know what to do. Can anyone please help me?