keyword planner, Avg monthly search is very high.
First of all, those numbers are ESTIMATES and include various match types (The fact that they are rounded is a good indicator of this!).
Next up, to get close to those impressions, you're going to have to be on the first page of search results and have a non restricted budget. You're likely not the only one competing for that keyword.
Check out your search impression share report to see how much of the traffic you're actually missing out on because of your bid, quality score etc.
Keyword planner is showing you the average number of searches made by the users which is actually calculated for full year. So it's an aggregated value. Most importantly it's only for the Exact keyword and not any other match type is included for this metric.
However number of clicks, impressions might vary because the tool takes into consideration your keyword matching options as well.
You can refer to this hel center article for more details: https://support.google.com/adwords/answer/3022575?hl=en