Now my question is, is it good for my future that I have sold my altcoins and invested in bitcoins?
Let's say usually, at first, when you're new to this world you buy several altcoins, then you realize many of them are pointless and it's better to focus on BTC, so I would say you made the right choice. The only altcoins I really like are ETH and BNB, those have a great potential and it's worth having some, especially ETH in the short term it may even outperform BTC.
That's what he have learned as well. I think he mostly bought shitcoins considering that he have sold everything he have and bought bitcoin instead. Some might say to never put your egg in one basket, however if that one basket has more potential in multiplying your egg in a couple or so years than those other baskets and not only that it's less riskier as well than those others, without a doubt I'd do the same as what the OP did.
I agree about ETH or BNB or some other handful of top alts in the market, but I'd always choose bitcoin over everything.
Now, the OP only needs to wait and be patient which doesn't bear much of a stress than watching your alts going up and down without the assurance of it bouncing back at some point if a whale suddenly dump his massive bag and people follow suit, that would definitely be an absolute disaster.