Update: I made a new Ubuntu 18.04 server and went through the process again from scratch, and the restore process worked perfectly, no mention of missing 'boto' module. I was able to fully download my backup, and restore a site (though I still got the same permissions warning when importing the database using wp-cli -- see below).
Then, I made another fresh Ubuntu 20.04 server and tried again. When I tried to download the backup the first time, I again got an error that the 'boto' package was missing, so i had to do what I mentioned above. Then I was able to continue with the process for a successful restore.
I tried this once again, just in case I had made a mistake, and again, missing 'boto'.
Maybe this is a problem specific to Hetzner Cloud -- I haven't tried on another host yet. Cristhian, if it would help, I can make you an instance to try.
For now, I'll just avoid Ubuntu 20.04.
More info on the db import error:
ERROR 1044 (42000) at line 22 in file: '/var/www/backup-db/webinoly-backup-db_domain.org_2020-07-27-08:30:02.sql': Access denied for user 'domain_org'@'localhost' to database 'domain_org'
ERROR 1044 (42000) at line 24 in file: '/var/www/backup-db/webinoly-backup-db_domain.org_2020-07-27-08:30:02.sql': Access denied for user 'domain_org'@'localhost' to database 'domain_org'
Lines 22 and 24 are:
22: CREATE DATABASE /*!32312 IF NOT EXISTS*/ `domain_org` /*!40100 DEFAULT CHARACTER SET utf8 */;
24: USE `domain_org`;
It must just be that the webinoly export includes the 'create' entries where the wp-cli export doesn't.