因为 Ubuntu 22.04 默认仓库没有 PHP 7.4,你可以用 ondrej/php PPA:

sudo apt update
sudo apt install software-properties-common -y
sudo add-apt-repository ppa:ondrej/php
sudo apt update
sudo apt install php7.4 php7.4-fpm php7.4-cli php7.4-mysql php7.4-curl php7.4-gd php7.4-mbstring php7.4-xml php7.4-zip -y

启动并设置开机自启:

sudo systemctl enable php7.4-fpm
sudo systemctl start php7.4-fpm
systemctl status php7.4-fpm

配置 Nginx 使用 PHP 7.4
修改站点配置 /etc/nginx/sites-available/default:

location ~ \.php$ {
    include snippets/fastcgi-php.conf;
    fastcgi_pass unix:/run/php/php7.4-fpm.sock;
}

测试配置并重载:

sudo nginx -t
sudo systemctl reload nginx

测试

新建测试文件 /var/www/html/info.php

<?php phpinfo(); ?>

浏览器访问:

http://你的树莓派IP/info.php