Get your debugging tools warmed up 
- FreePBX 16 won’t currently install using PHP 8:
STARTING ASTERISK
Asterisk Started
Assuming you are Database Root
Checking if SELinux is enabled…Its not (good)!
No /etc/asterisk/asterisk.conf file detected. Installing…Writing /etc/asterisk/asterisk.conf…Done
Checking if Asterisk is running and we can talk to it as the ‘asterisk’ user…Yes. Determined Asterisk version to be: 18.4.0
Checking if NodeJS is installed and we can get a version from it…Yes. Determined NodeJS version to be: 14.17.1
Preliminary checks done. Starting FreePBX Installation
Checking if this is a new install…Yes (No /etc/freepbx.conf file detected)
Database Root installation checking credentials and permissions…Connected!
PHP Fatal error: Declaration of FreePBX\Database::query() must be compatible with PDO::query(string $query, ?int $fetchMode = null, mixed …$fetchModeArgs) in /usr/src/freepbx/amp_conf/htdocs/admin/libraries/BMO/Database.class.php on line 239
FreePBX installation failed!
But it does install and run ok with the latest framework and PHP 7:
fwconsole ma list | grep framework
| framework | 16.0.10.11 | Enabled | GPLv2+ |
root@FreePBX:~# php --version
PHP 7.4.20 (cli) (built: Jun 4 2021 23:22:32) ( NTS )