I gave up the installation for now because I encountered a lot of errors during the previous installation.
Today I have figured it out and share it here.
It may be difficult to understand because I use the translation software.
Notice the error in Composer.
I didn't notice that "proc_get_status" was disabled when Composer was installed earlier. I noticed this time and changed "php.ini".
Change ".conf".
On my server, Nginx has two .confs, I don't know if it's the same as yours. One is located in /usr/local/nginx/conf/rewrite/flarum.conf and one is located in /usr/local/nginx/conf/vhost/XXX.com.conf.
I added "include /path/to/flarum/.nginx.conf;" to /usr/local/nginx/conf/rewrite/flarum.conf
Find the line "root /XXX/XXX/XXX" in /usr/local/nginx/conf/vhost/XXX.com.conf and add "/public" at the end.
You're done!