I once wrote a post about it (in German) https://peakd.com/hive-121566/@stayoutoftherz/ist-rapsol-giftig
Reason is it´s content of erucic acid which damages the heart muscle. In the past canola oil was therefore only used for industry use (lamp oil, etc), and only since breading variants of low acid content its success in food industry started. Nowadays up to 2% erucic acid is allowed in canola oil. FDA says it is safe, but it is quite concerning in how many products canola oil is, even in oat milk.