Have you checked if your language and keyboard layout support suggestions? Some layouts only show suggestions on the touch keyboard.
To fix it, go to Settings > Time & Language > Typing and make sure Show text suggestions when typing on the physical keyboard is on. Then go to Settings > Time & Language > Language & Region, select your language, click Language options, and use Microsoft IME or a supported keyboard. If needed, remove and re-add the keyboard layout and restart your PC to refresh the suggestions.