.. when bitcoin will be dumped and the money will come into altcoins.

you don't understand if bitcoin dumped, the altcoin will be dumped 10x.
Good luck, happy waiting.

.. if there will be a huge hyip on the market like it was in the start of 2018

Monero isn't one of them (ICO and Defi project)

..and now I see that very few people are interested in investing in privacy coins, so I'm not sure the price Monero will hit ATH like it did in 2017.

How many mixing services to hide your transaction?. If you use Monero you don't need that.