Back in June, in Upgrading Debian to version 13, I wrote:

Next step: Upgrade Ubuntu 24.04 (which I am using right now) to 26.04. I will wait for Canonical to publish an official procedure for this, which IIRC is supposed to happen in July.

It is now September. I got tired of waiting. I installed 26.04 on my other old HP desktop., replacing the 25.04 version previously installed. My data drives are external, so after shutting down both the old and the “new” system I uuplugged them from the 24.04 box and plugged them into the 26.04 system. This worked fairly well. The USB drives all showed and I was doing fine until I tried running my backup scripts. These all failed.

The problem was that on 24.04 the path to a USB drive looks something like /media/gmcdavid/BACKUP3. On 26.04 it is /run/media/gmcdavid/BACKUP3. So I had to add /run where these drives were being referenced. Fortunately there were only a few such cases. After theose changes the backup scripts worked correctly.