[SOLVED] No real problem yet, I need security for a new server on my Raspberry pi 4

I'm assuming this is the right place, I recently set up my raspberry pi 4 server installed apache2 php, and now I find out I understand I need some sort of security. Ant suggestions?

Welcome to LQ!

A firewall at minimum.

Aside from changing the default passwords before setting it out on the net, it is mostly locked down. Firewalls can be an amusing way to spend time but at the end of the day you'll have to let in port 22, 80, and 443. Ports 80 and 443 are where PHP will be available, so that is where you should focus your attention. The main thing there is to ensure that all input is sanitized and validated when writing with PHP or other languages. See the programming concept of tainted data. But if you would like a guide, then the OWASP Top 10 Web Application Security Risks would be a good start.

You should also ensure that updates are installed regular, I recommend 1 time a day. You might also think about setting up unattended-upgrades.

fail2ban is your friend here.

In addition to these other excellent suggestions, block all incoming ports in your router except for the ones you must have open for the server to function.

Also, you might want to run an AV. In this usage, ClamAV should be suitable.