Apache 2 php-fpm on LMDE 7, local environment throws error “Permission denied: AH02454: FCGI: attempt to connect to Unix domain socket” (PHP 8.4)

Recently I installed Linux Mint Debian Edition 7 over my old Debian 11. So far a good choice for me, but I can’t get my local dev environment to work again.

What I want to achieve:
A local webserver that lets me run static sites and sites with php. I don’t need any databases, and one fairly recent version of PHP is enough. The sites are in my home folder and belong to my user, and I want to keep it that way since I need to be able to work on them.

How I used to have that set up:
On my old system I had apache2 installed, along with I think several versions of PHP via Ondrej repositories which I actually never used. I used to put symlinks to each site in /var/html/www, and /etc/apache2/sites-available/000-default.conf looked like this:

<VirtualHost *:80> ServerName example.com ServerAlias www.example.com DocumentRoot /var/www/html <Directory /var/www/html> Options -Indexes +FollowSymLinks +MultiViews AllowOverride All Require all granted </Directory> <FilesMatch \.php$> # 2.4.10+ can proxy to unix socket SetHandler "proxy:unix:/var/run/php/php7.4-fpm.sock|fcgi://localhost" </FilesMatch> ErrorLog ${APACHE_LOG_DIR}/error.log CustomLog ${APACHE_LOG_DIR}/access.log combined </VirtualHost>

Then I changed the lines in /etc/php/7.4/fpm/pool.d/www.conf that showed the user and group www-data to my user, that’s four lines in total:

user = myname group = myname listen.owner = myname listen.group = myname

I also changed the user and group in /usr/lib/tmpfiles.d/php7.4-fpm.conf. As far as my (old) notes go, that was all I did.

What I did now:
On the new system I installed apache2, libapache2-mod-fcgid, php-fpm and a bunch of modules using apt with no extra repositories, so now I have PHP8.4. Made the same username changes as above, just in the analogous 8.4 files, and made the VirtualHost config file the same except with SetHandler "proxy:unix:/var/run/php/php8.4-fpm.sock|fcgi://localhost".

Result: Static websites work fine, anything with php says 503 Service Unavailable and creates the following entries in /var/log/apache2/error.log:

[Wed Dec 10 16:48:20.407597 2025] [proxy:error] [pid 16091:tid 16119] (13)Permission denied: AH02454: FCGI: attempt to connect to Unix domain socket /var/run/php/php8.4-fpm.sock (localhost:8000) failed [Wed Dec 10 16:48:20.407635 2025] [proxy_fcgi:error] [pid 16091:tid 16119] [client 127.0.0.1:38804] AH01079: failed to make connection to backend: localhost

So something is wrong with my permissions, but I have no idea what? I will readily admit that I don’t really know what all these things mean in detail, so I would be super grateful for any pointers!