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Using a different port is done by changing the port when restoring your site. Please note that the hostname matters. localhost always connects using a named pipe, 127.0.0.1 always connects using TCP/IP. This is how all MySQL software works and we have documented it anyway.  You can access the documentation by clicking the documentation icon at the top of the Restore Database page; it open in a new tab/window.

Regarding your error, it comes from your server which is misconfigured. You have set up a MySQL configuration option which requires a primary key on all tables in the database. Joomla does not have a primary key on all tables. Therefore your MySQL server configuration is incompatible with Joomla. That's why you are getting an error restoring the core j_utf8_conversion table. If we worked around that on restoration your site would still be broken after the restoration is finished.

You need to change your MySQL server configuration to not use the sql_require_primary_key option. A cursory Google search (took me about 10 seconds) on your error message yields a simple solution: https://stackoverflow.com/questions/66149804/change-sql-require-primary-key-value-permanently-in-mysql-8

The key difference between MySQL 8 and 5 is that MySQL 8 has sql_require_primary_key set by default whereas MySQL 5 doesn't. That's why I pointed you towards that direction.

For what it's worth, my local development server is on MySQL 8.0 using that change and another change about using legacy passwords by default (since Joomla 3 can't support anything else).

Joomla 4 has added a primary key to every core table. The most recent versions of our software have followed suite. I cannot vouch for third party extensions.

BTW you are right that removing the need for a primary key breaks replication. That's exactly why it was made a requirement in MySQL 8!

Your problem isn't that Digital Ocean is not goo enough for Joomla but the fact that Joomla 3 is a 12-year old architecture (first released 9 years ago) created before any of these considerations made any practical sense. Joomla 4 at least takes all of that into account. Hopefully 2021 will be the year of Joomla 4.

Regarding your request, it's something I did consider, briefly, before realising it's a pipe dream :(

We cannot add a primary key to tables indiscriminately. It will break things. Doing that for our own software required going through each table which didn't have a primary key and consider how it's used, should we make an existing column a primary key, should we make a column group a primary key or should we add a new column and make it a primary key. This cannot be automated in any sensible way.

For example, n-to-n relation tables ("glue" tables) can usually use the two foreign keys as a primary key group since you cannot assign the same record from table B to the same record form table A multiple times. If, however, this is possible because of a denormalised schema (the glue table contains more than FKs, i.e. you can now have multiple instances of an item described by a table B record assigned to the same record in table A) you can't do that. You will have to put more keys into the group or refactor the code.

Unless you know the intent of the table structure you can't make these decisions. The intent is not conveyed at all, let alone in machine readable format. You need to study the extension code to figure it out.