There's no government restrictions preventing you from assembling elsewhere.

Your interpretation would make shutting down any place where people assembled unconstitutional which was clearly never the intent.

Of course you can. Nothing stops the same group of people from congregating on Discord, Rumble, or even in real life.

This is like saying that closing all churches of a religion is not a big deal as the people can perfectly pray by themselves. (Also since they can pray in their head why not making that religion's prayers illegal to speak aloud)

No, it's like saying it's not a big deal to close one particular church building with eminent domain to build a railway station there.

If you used to assemble at a public park, and the city closes the park entirely to turn it into something else, does that violate your right to assemble too?

If the specific intent was to make it difficult to assemble, then yes.

The law hasn't made it difficult to use alternatives to tiktok, which are free and numerous.

depends. Was it the de facto town square?

Even if it was the town square, if the property went from public to private ownership property ownership laws trump your free speech laws. You cannot come on to my properly and say whatever you want, more so you can't say it's not trespassing because of freedom of speech.

If the city sold the public property with the specific intent of having a private entity stop protected speech they were powerless to stop then yes, it would be a free speech issue