The list of games you can spectate via Multiplayer - Observe only finds very low Elo matches. I couldn’t find a single match over 800 Elo. Would be nice if you could also find games above average Elo (<1000) to spectate, which you can in games like AoE2. As it is the feature is near useless (like most features in the game unfortunately: replays, observer interface etc.).
Searching by Elo is a nice suggestion! I’ll take it to the team.