Platforms don't care about you (or your brand)
They care about the money you give to them.
They will eventually keep decreasing your reach to the audience you built. Why? Because they can, and they don't want to show your posts to your audience, they want to show more ads to them.
The point of building an audience is to make them part of your "community/brand/etc", but if they don't see your messages, what's the point of building it?
So the earlier you realise that you need to build your own fort and get people inside it, the better results you'll see.
Some common/uncommon ways to build your fort:- – Create an E-mail list:- Hit the "send" button and everyone in your list will get that mail, now atleast it's their choice if they want to open it or not.
Create a WhatsApp Broadcast:- You remember all those SMS's we used to get from different companies? I feel WhatsApp can replace that. If done in a non-annoying way, you can reach to everyone who choose to subscribe your "Broadcast List".
Use Discord:- Discord is like one powerhouse to keep your community alive. Make it interesting, and people will stay.
The main point is, it's better if you realise that marketing is not about spending money, it's about spending less money.