The Compliance tab explains the check every ad goes through. Ads are scanned the moment they are written and again whenever you edit them. Things that would likely get an ad rejected (personal attributes, unrealistic claims, banned phrasing, wrong formatting for the network) are flagged; anything blocked cannot be created until it is fixed.
Ads the networks turned down: once a day ADs reads Google (through the direct connection or your Google Ads script) and Meta for any ad they did not approve, and lists it here with the network's reason in plain words. Press Check now to read them straight away. Then fix the ad in that network's ads manager and ask for a review.
When a reason names words, record them under "What it has learned from your rejections": copy the words exactly as they appeared. ADs flags those words next time.
This is a safety net, not a guarantee of approval and not legal advice. The networks change their rules and the final decision is always theirs.