rc.local is a very convenient method of firing off a process when the system is booted. It is being phased out.

To replace it you can do the following:

create a file named /usr/lib/systemd/system/StartupService.service 

[Service]
Type=forking
TimeoutSec=0
RemainAfterExit=yes
ExecStart=/usr/local/sbin/StartupScript start

[Unit]
Description=rc.local replacement
CondidtionFileIsExecutable=/usr/local/sbin/StartupScript
After=network-online.target

Wants=network-online.target

[Install]
WantedBy=multi-user.target


replace /usr/local/sbin/StartupScript with whatever binary or script you want to run on boot

now execute:

systemctl enable StartupService

The lines:

After=network-online.target

Wants=network-online.target

causes it to wait to start the targeted script until after the network is started

This was tested on Fedora 33