Pi Server - How to Sync over WLAN

I’m new to Nextcloud and would like to install it on a Rasberry Pi Server and then sync my MacOS and IOS files over my wireless network. I do not wish my files to be accessible to the WAN.
Is this possible? and if so please advise how to assign the pi a dedicated ssid to which the IOS/MACOS devices can connect

I think you’re misunderstanding network technology. If you’ve connected your Raspberry Pi to your LAN, you should directly be able to access it via your WiFi using and ip address or the configured dns name. There is no need to assign any “dedicated” SSID, that’s not how a network works.