he arreglado el problema del PID y ahora arranca el servicio de Nextcloud

Dockerfile

@@ -21,6 +21,8 @@ RUN tar xvjf nextcloud-22.2.0.tar.bz2
 COPY php-fpm.conf /etc/php/7.4/fpm/php-fpm.conf
 COPY www.conf /etc/php/7.4/fpm/pool.d/www.conf
 
+#RUN service php7.4-fpm start
+
 # Vamos a la carpeta nextcloud recien creada, ponemos el puerto y creamos un volume para indicar luego la base de datos
 
 WORKDIR nextcloud

php-fpm.conf

@@ -15,8 +15,8 @@
 ; Note: the default prefix is /var
 ; Default Value: none
 ; Warning: if you change the value here, you need to modify systemd
-; service PIDFile= setting to match the value here.
-pid = /run/php/php7.4-fpm.pid
+;service PIDFile= /tmp/php7.4.-fpm.pid
+pid = /tmp/php7.4-fpm.pid
 
 ; Error log file
 ; If it's set to "syslog", log is sent to syslogd instead of being written