nginx try_files php file is not parsed - php

Question

My project was split into three projects for historical reasons
This makes the nginx configuration file exceptionally difficult to handle, so much that I have tried many solutions and still haven't solved it perfectly.
Directory configuration:
/var/www/html/: project directory
/mnt/a.com/: another project directory
The third project uses a reverse proxy
The configuration file is as follows:
server {
listen 80;
listen [::]:80 default ipv6only=on;
server_name _;
root /var/www/html;
index index.html index.htm index.php;
sendfile off;
location / {
try_files $uri $uri/index.html $uri/index.htm $uri/index.php #mnt;
# try_files $uri $uri/ #mnt;
# This annotated code causes a 403 error to be returned when accessing an empty directory instead of redirecting to #mnt
}
location #mnt {
root /mnt/a.com;
try_files $uri $uri/index.html $uri/index.htm $uri/index.php #proxy;
}
location #proxy {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://a-proxy.com;
}
location ~ \.php$ {
try_files $uri #mntphp;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass 127.0.0.1:9000;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
fastcgi_index index.php;
include fastcgi_params;
}
location #mntphp {
root /mnt/a.com;
try_files $uri #proxy;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass 127.0.0.1:9000;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
fastcgi_index index.php;
include fastcgi_params;
}
# deny access to . files, for security
location ~ /\. {
log_not_found off;
deny all;
}
location ~* \.(jpg|jpeg|gif|png|css|js|ico|webp|tiff|ttf|svg)$ {
expires 2d;
}
error_log /var/log/a.com_error.log;
access_log /var/log/a.com.log;
}
But such a configuration will cause the php file to fail to parse. I know this is because try_files will redirect only the last parameter, but I don't know how to solve this