To say that a stock is at a record high the metric you should look at is price of the stock divided by the earnings the stock is expected to generate in the future. Earnings the stock is expected to generate in the future is a forecast and it’s going to be subjective. You can use trailing earnings, or shiller earnings as a proxy, or try something more complicated.
Stocks are at a high though not a the highest they have ever been. Therefore they are overvalued by this historically looking metrics. In order to believe they are not overvalued someone needs to believe the earnings in the future will be about double what they currently are generating. And the narrative you may hear for why earnings will be double in the future compared to what they are currently is beliefs about AI and its impact on efficiency.
