Restore old myISAM tables from physical files

[Stewart Lawrence]

Hi Folks.
I have been working with a set of MySQL databases for near on 20 years. These are supporting a LAMP-style server running numerous websites. In the past, I have been able to just copy the directories containing the data files from version to version. Though there have been some issues with this, it has 'got me through' and being somewhat lazy / time constrained I have used file-based backups and not sql dumps as my backup strategy.
My current approach is to have the web server running in my DMZ on Ubuntu. The MySQL database is housed on a Mac Mini server inside my network, accessed through pinholes in my firewall. A successful approach for the last 12+ years.
I admit that this has been a bit of a clumsy upgrade path and it shows my lack of due-diligence in performing the upgrade. What I face now is that I have upgraded the web server and the MySQL client to Ubuntu 18 and MySQL client 5.7. I have upgraded the Mac Mini to MySQL 8.0. I have successful data connection between the Ubuntu Server and the Mac Mini Server.
My issue is that the database server does not have the data contained in it to support the websites. I need to upgrade / import the data from the old tables in the directories into the new MySQL 8.0 server. I have tried a number of things including doing a CREATE DATABASE xyz and then dropping the data into the xyz directory, starting the server and no automatic upgrade. I have then tried a manual upgrade which did not find any data tables.
NOTE: I have set permissions on the data files to the MySQL user and group. I have set the permissions to 750 (using chmod) as per the instructions for 8.0 since it requires exclusive access to the data files.
Does anyone have any experience in this area? I realise I have been dumb in my approach but I am hoping that there is a knight on a white horse that can save the day.....

Stewart