How can I permanently assign a static IP address to Wi-Fi clients? (Lineage OS 17.1 Android 10)
DHCP  is Dynamic Hosting Control Protocol. It give you dynamic IP address. Static IP address you need to lease. DHCP server give ip address to host, it is not static.
You can assign IP address. Go to setting / connection / select network / manage network setting / Advance option. Here you can give static IP address.
After Question Update.
Go to Wi-Fi / setting / Advance networking / DHCP IP reservation / Here add static IP address and also select device for static IP address.
Network admin use static IP address for shared device like ZEROX machine printer.