Tried building the Dockerfile directly as that seems to be the only semi-official support, but ran into various issues. I'm on ARM, so can't use zknt as others have mentioned. Switched to another Pixelfed image murazaki/pixelfed:edge-apache; but get the following error:
pixelfed-app | PHP Warning: require_once(/var/www/bootstrap/app.php): Failed to open stream: No such file or directory in /var/www/artisan on line 20
pixelfed-app | PHP Fatal error: Uncaught Error: Failed opening required '/var/www/bootstrap/app.php' (include_path='.:/usr/local/lib/php') in /var/www/artisan:20
pixelfed-app | Stack trace:
pixelfed-app | #0 {main}
pixelfed-app | thrown in /var/www/artisan on line 20