Nginx subdirectory root PHP with Rails or Django app - nginx

Question

I'm trying to add a PHP app in subdirectory with different root location.
For example, I have a Rails app at root / and I want to add a phpBB forum at /forum location.
I also have a specific need: I want to add a rewrite rule for a file located in forum root directory (e.g. rewrite /forum/foo.php to /forum/bar.php)
I tried multiple configurations with some examples given on stackoverflow but none of the solutions work :(
If there is no solution I will use subdomain instead (e.g. forum.domain.com), but I would like to try with only one domain if possible
upstream railsApp {
server unix:/tmp/puma.sock;
}
server {
listen 80;
server_name domain.com;
return 301 https://$server_name$request_uri;
}
server {
listen 443 ssl http2;
server_name domain.com;
root /var/www/domain.com/railsApp/public;
ssl_certificate /etc/nginx/ssl_certs/domain.com/fullchain.pem;
ssl_certificate_key /etc/nginx/ssl_certs/domain.com/privkey.pem;
client_body_buffer_size 10M;
client_max_body_size 10M;
location / {
try_files $uri #proxy;
}
location #proxy {
include proxy_params;
proxy_pass http://railsApp;
}
# Here I want a PHP app with different root location
# forum is an example
location /forum {
root /var/www/other-location;
index index.html index.php;
include proxy_params;
location ~ \.php$ {
fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}
# I also want to add rewrite rule for a specific file name
location ~ /foo {
rewrite ^(.*)$ /bar.php$1 last;
}
}
}
Thanks