Ah, great news! Very glad all your DBs are alive again.
You can tell MySQL 8.4 to use the old password plugin for the root user, thereby allowing old PHPs such as 7.2 to connect. I've put together a tiny stack to demo this for you. It has:
- mysql 8.4
- php 7.2
- nginx to host the single file site (you'll need to point it at the location of the site on your mac)
Inside the stack bundle is the appropriate my.cnf override to add mysql_native_password=ON.
Once you start this test stack, check out https://testing.test — you should see failures success messages.
Ignore from here down; see follow-up post below.
Next connect to the new MySQL 8.4 in Sequel Ace, select the mysql database, and locate the root user in the user table. If you scroll far enough you'll find the plugin column which will contain caching_sha2_password. Don't change this directly; you need to run the following SQL in Sequel Ace's "Query" tab to do so cleanly:
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';
FLUSH PRIVILEGES;
Now reload https://testing.test; you should see "Connected successfully" and Sequel Ace will show mysql_native_password as the plugin for the root user.
Let me know how you go!