nginx

upstream php_fpm {
	server unix:/run/php/php8.1-fpm.sock;

	keepalive 10;

	# Equal to PHP's `pm.max_requests`
	keepalive_requests 500;
}

##
# Cache setup
##
fastcgi_cache_path /usr/share/nginx/fastcgi_cache levels=1:2 keys_zone=WORDPRESS:10m max_size=1g inactive=1d;
fastcgi_ignore_headers Cache-Control Expires;

# To be able to cache ActivityPub responses separately
map $http_accept $vary_key {
	default "default";
	"~application/activity\+json" "json";
}

##
# Server configuration
##
server {
	# Update for your specific server (name, ports, SSL termination, etc.)!
	listen 80;
	listen [::]:80;

	server_name example.org;

	client_body_buffer_size 10K;
	client_header_buffer_size 1k;
	client_max_body_size 8m;
	large_client_header_buffers 2 1k;

	client_body_timeout 12;
	client_header_timeout 12;
	keepalive_timeout 15;
	send_timeout 10;

	root /var/www/html;

	index index.html index.htm index.php;

	location / {
		try_files $uri $uri/ /index.php?$args;
	}

	location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg)$ {
		expires max;
		log_not_found off;
	}

	# Pass PHP scripts to FastCGI server
	location ~ \.php$ {
		# Caching is on by default
		set $skip_cache 0;

		# Don't cache the following URLs
		if ($request_uri ~* "^/wp-") {
			set $skip_cache 1;
		}

		# But do cache GET requests to ActivityPub endpoints
		if ($request_uri ~* "^/wp-json/activitypub") {
			set $skip_cache 0;
		}

		# Don't cache logged in users or commenters
		if ($http_cookie ~* "comment_author_|wordpress_(?!test_cookie)|wp-postpass_") {
			set $skip_cache 1;
		}

		# Don't cache POST requests
		if ($request_method = POST) {
			set $skip_cache 1;
		}

		# Note the `$vary_key` part
		fastcgi_cache_key "$vary_key$scheme$request_method$host$request_uri";
		fastcgi_cache WORDPRESS;

		fastcgi_cache_bypass $skip_cache;
		fastcgi_no_cache $skip_cache;

		fastcgi_cache_valid any 15s;

		# Misc. additional settings
		fastcgi_cache_use_stale error timeout updating http_500;
		fastcgi_cache_background_update on;
		fastcgi_cache_lock on;
		#fastcgi_cache_lock_timeout 10s;
		fastcgi_cache_lock_age 5s;

		# All things PHP
		include snippets/fastcgi-php.conf;
		fastcgi_intercept_errors on;
		fastcgi_keep_conn on;

		fastcgi_pass php_fpm;

		include fastcgi_params;

		add_header X-FastCGI-Cache $upstream_cache_status;
	}
}

Not sure if the buffer size and timeout directives really add anything. At one point, I was just trying out about anything I could find.

And even if they do, I might actually move them out to a more generic config file.

Added in the keepalive bits. Again, :-D not sure if needed, or if it even improves performance (at all).