Bueno, parecía prometedor, pero cuando hice clic en “ver sitio” para volver a la página principal del índice, se bloqueó. 
Del registro de php-fpm:
[27-Feb-2025 15:21:37 UTC] PHP Fatal error: Uncaught Error: Call to undefined function WPDiscourse\\Shared\\mb_convert_encoding() in /wordpress/wp-content/plugins/wp-discourse/lib/template-functions.php:335
Stack trace:
#0 /wordpress/wp-content/plugins/wp-discourse/lib/discourse-comment-formatter.php(136): WPDiscourse\\DiscourseCommentFormatter\\DiscourseCommentFormatter->fix_avatars_in_quotes()
#1 /wordpress/wp-content/plugins/wp-discourse/lib/discourse-comment.php(312): WPDiscourse\\DiscourseCommentFormatter\\DiscourseCommentFormatter->format()
#2 /wordpress/wp-content/plugins/wp-discourse/blocks/comments/comments.php(34): WPDiscourse\\DiscourseComment\\DiscourseComment->comments_template()
#3 /wordpress/wp-includes/class-wp-block.php(537): render_block_wpdc_comments()
#4 /wordpress/wp-includes/class-wp-block.php(517): WP_Block->render()
#5 /wordpress/wp-includes/class-wp-block.php(517): WP_Block->render()
#6 /wordpress/wp-includes/blocks/post-template.php(123): WP_Block->render()
#7 /wordpress/wp-includes/class-wp-block.php(537): render_block_core_post_template()
#8 /wordpress/wp-includes/class-wp-block.php(517): WP_Block->render()
#9 /wordpress/wp-includes/class-wp-block.php(517): WP_Block->render()
#10 /wordpress/wp-includes/blocks.php(2191): WP_Block->render()
#11 /wordpress/wp-includes/blocks.php(2243): render_block()
#12 /wordpress/wp-includes/block-template.php(263): do_blocks()
#13 /wordpress/wp-includes/template-canvas.php(12): get_the_block_template_html()
#14 /wordpress/wp-includes/template-loader.php(106): include('...')
#15 /wordpress/wp-blog-header.php(19): require_once('...')
#16 /wordpress/index.php(17): require('...')
#17 {main}
thrown in /wordpress/wp-content/plugins/wp-discourse/lib/template-functions.php on line 335
Edición 1: Dice función indefinida mb_convert_encoding(). ¿Quizás solo necesito instalar un paquete de PHP que falta?
Edición 2: Sí, eso es todo. Necesitaba instalar php-mbstring. Todo parece estar funcionando ahora. ¡Gracias!