I argue here that preventing a large iceberg from melting is absurdly cheap per unit area compared to just about any other way of making new land, and it's kind of crazy to spend money on space exploration and colonization before colonizing the oceans with floating ice-islands.
You can't really make a great new nation, startup city or network state in secret. You have to advertise it.
And if you are doing it against the wishes of the local government, that will discourage people from coming. This kind of effect even works if the locals are militarily weaker than you. Look at Israel!
Now there are some places where startup cities/communities are happening. Prospera is an example. But that requires some quite specific circumstances and isn't replicable. Legacy governments just don't want to give up control of their land. Another example is Liberland. Liberland could potentially be pretty good but Croatia hates it and they send police there to trash it even though they don't have a legal claim on the land.
If you want a nation-type org without the land you can start a cult or a religion. Mormonism sort of did this but they are ultimately still ruled by the US central government and it is gradually destroying them. If Mormonism was happening on an island it would be much more robust. Scientology is another example. They have their own compounds and own parts of various cities in the USA and the UK. Religious groups like The Amish are a further example - they use language and religion as barriers to keep foreign ideas and people out, but I don't think that is replicable at scale today because there's a decent chance that legacy governments would shut you down. So you can avoid the need for land to some extent but you will pay a large price.