The number of investors should be expected to increase, because the ETF approval was implemented for large investment purses like corporations and big companies and even for individuals with large pockets.
Also is the case of the bull run which normally happens after the halving to be in effect. The bull run season is a time when demand gets higher and profits are made from quick trades.
Although, it would be that the ETF is the major innovation prior to the halving event, the rise in price and demand for other crypto currencies, tokens and altcoins compete with the throve of those interested in long term holding investment that BTC is sure to provide.

With Bitcoin's current popularity, there is a possibility that more investors will invest in it. The halving event will attract them to find out more about it. At least, that's what smart investors do.
They will not immediately invest their money in Bitcoin but will find out more before investing in Bitcoin. There may be more and more new investors when the price of bitcoin starts to increase, and if the price can reach $100k, these new investors will start investing in bitcoin. The incident will probably be the same as in previous years, where there will be many disappointed investors, and there will be investors who make big profits.

because when it comes to new investors, they cannot be identified. because those who only come for the halving may not necessarily have a really strong interest when the storm occurs.
we will see them come and go. some who are serious about investing in Bitcoin will remain high, and most others will abandon their investment even without the results they expected.
but I believe, there will be more old investors who remain than those who have just arrived. those who are new do not necessarily have the knowledge. and those who can survive I am sure are investors with knowledge.

Halving is just the end of a cycle and the start of a new one. Yes, the reward is reduced by half, but it's not the first halving and there's no surprise that this is how Bitcoin works. So, as such, I think it doesn't have any direct impact on attracting or scaring off investors. But Bitcoin does get some media attention due to halving, and attention is generally good to remind potential investors that Bitcoin exists.
There's no reason for a number of new investors to decrease, as halving makes Bitcoin more scarce, which is in principle good for investments.

No, but the opposite will happen.
Obviously, many already said to other people that we are entering the bull run a few months after the halving event. This kind of narrative is what investors will thin hence, they will try to enter the crypto market and will buy Bitcoins and other coins to ride the train, and get some profits just by buying the token.

I can't think of any reason why new investors will decrease knowing that they "MIGHT" earn money if they will invest their money during the bull run. The halving event is just an event, but that will be a main catalyst towards the increase in the price of Bitcoin and when new investors heard that they might earn more money through buy and hold during the bull market, they will come and take the opportunity.

I don't know if there was a time where the total of new investors decrease because I always believe that new investors are coming up day after day after day.

This is just obvious people gamble with their investment and they're not even called investors cause they come and go. Definitely people with this mindset will leave and hope for another ATH or halving but I'm believing a time will come when people like this will regret after seeing the price of bitcoin or probably when it's time to buy they'll not be able to buy more compared to bitcoin price back then. No one can really tell when it comes to price speculation but we always have a certain believe or else no one will think of investing, op will have to make a research in terms of population before and after the halving but I don't think short term traders will love to sell now due to the price

I thought we are still in the halving. And I also thought the halving will stay up to a month. Is it that the halving was just a day? That's not withstanding, many investors came to the ecosystem because of the halving and some were thinking that in the halving bitcoin would reduced for them to invest more but the price was stable and it was after the two days of the halving the price slightly reduce and after some days it goes back. And even the time when bitcoin price goes down, the transaction fee didn't allow people to buy because it was too high and people were disappointed about the whole season.

But that will not stop people to invest in Bitcoin before the next halving of 2028.  And in my own observation, the number of investors that will come up in the period will be more than the previous season. People have seen the important of bitcoin so many people will like to invest in Bitcoin for retirement and others.

Investors aren't attracted exactly by the event but they are attracted by the gains they can potentially get from the investments that they make before the halving because history shows that Bitcoin tends to go higher after the halving event, so just because the event is gone, it doesn't mean investors will reduce or people wouldn't invest anymore because we are yet to see the effects of the halving event and the bull run is yet to be seen.

It will probably take some time for it to happen, and until then, we can expect new investors to keep joining because we are still at a reasonable position if someone wants to make an entry because as per expectations, the price of Bitcoin should at least go around $100k, it might go higher than that.

For people like me, I am not so worried about the trend of the moment, rather than investing for the future. Rushing into investing in Bitcoin for the sake of halving might not be the best way to go about investments in Bitcoin even though it might not necessarily mean a failure, however it is always best advised to invest at a convenient time, whether halving or not so that you don't lumpsum and become disappointed expecting some humongous figures as a return. My opinion and decision about bitcoin investment is convenience and knowledge. Knowledge in the sense that, one needs to understand the prosperity of the market and uptrend and downtrend of the market and Convenience in the sense that, you invest gradually through the DCA approach with the amount you can afford,  and allow it to grow steady while we learn from the process