Thank you both for the responses - apologies for not replying sooner, but my power supply bit the dust the day after I posted and I used it as an excuse to do a complete rebuild, and between waiting for the parts and then finding time to reinstall and get my test server all set up again during a busy time of the year ... well, time flies.
I swapped from using xampp to laragon (my host uses mysql instead of mariadb which is now xampp's default, and while research is saying there's not much difference, that doesn't mean none, and I didn't want to have to try to untangle that when databases are still basically witchcraft as far as I'm concerned) and basically started again from scratch since I'd barely gotten started the first time. I made sure my settings were correct as per your advice, and whether that was it or not, it's working fine now!
With that out of the way, I'm looking forward to digging into the meat of flatpress customization

I really used to enjoy designing layouts back in the day, so I'm excited to re-learn design and styling for the modern multi-screen internet.
Thanks again!