stern - seemingly very serious strict - demanding that rules concerning behavior are obeyed and observed A person might be stern, or someone could give you a very stern lecture. A person can also be strict, but you can not have a strict discussion. However, rules and restrictions can be strict. Example: The president was very stern when he announced the strict lockdown regulations.

Stern means more like serious, kind of hard natured, while strict is more like tight to the rules and unforgiving, but they are pretty similar in my opinion. Hope this helps:)