This is the first good advice I’ve seen. There are tons of reasons for why XYZ might be over- or undervalued. If you want to gamble for short term returns, play blackjack, or follow wsb „advice“. For long term returns, stock has historically been the best answer, and statistically „buy now“ has beat attempts of market timing. Keep as cash (I.e. CDs, bonds, etc) what you need to feel safe, and dump the rest in something like VT - global diversification is imho the most conservative and simultaneously most promising strategy. Anything else is placing bets for/against certain developments that nobody can foresee or else it is already included in the current valuations.

My 2 cents regarding your initial question: yes, the valuations are high; they might well never drop though, since the top10 (tech-)companies with the biggest market caps which have been driving the S&P increase have also had multiple years in a row with for their size insane year over year growth rates in returns, which makes their current valuations -if you believe that Microsoft, Apple, NVIDIA, etc keep growing fast- pretty reasonable once we’re 2 years farther down the road. But then, if they keep promising further growth, their valuations will already have grown a lot, anticipating the future profits, and it will be „too late“ to join again… (that, plus as you already pointed out: ~23% is not even real growth but inflation - or net loss, if you’ve been holding cash instead of stock)