I can see the top 20 popular tags but is there a way to display all tags?
Yes and no... If you look here, you will see that the limit of the tags is hard coded and so you cannot simply change it.
The correct way would be to write your own plugin, something like a "AllTagsModule" plugin which basically would copy the code of the tag module and only change class name and a single line. You would would have to take care for displaying your module and ensuring that the other module isn't displayed in the plugin. Nothing too hard.
You surely can change that single line in the file, too, and maybe in this case it wouldn't be too bad. Normally I do not advice changing any core files. In this case, I'm uncertain which approach would make more sense.
Writing your own plugin would be a permanent solution and a solution which could be spread across more than one installation. So in the end I would prefer that.
I was thinking more of a way to simply be taken to a page that displayed all the tags but what you are saying would show them all. It begs the question, if a tag exists but is not within the limit of the top threshold, what good is it? If there is no way to search by it or interact with it then it sort of becomes useless. Maybe i am miss understanding how to use tags correctly. I was thinking of them as a way to connect disparate categories/threads/posts.
It is also possible to show a dedicated page with all the tags on it, but I wouldn't know of a way to present them so that it is not a boring list. But depending on the way you use tags, it might not be so useless as I think.
Creating a plugin that shows such a list would be really easy by the way. If you are interested and have a little knowledge I could guide you.
If you decide to take the challenge, start with this plugin: https://open.vanillaforums.com/addon/howtovanillapage-plugin
Customize it a little bit so that it shows texts which suit your needs and in the next steps I would show you how to
It would really be a good beginner plugin.
Thanks for your help, that answers my question. I probably won't create it since i'm lazy not a good developer but it would be a great idea for a plugin if someone else wanted to take it on.
I haven't seen that happen too often (that someone is writing a plugin just because it is a good idea).
By the way: that you are not a good developer is no excuse, since you would find it to be quite easy. But lazyness is a very good reason in this case
how you do that? is there an api call?
If you look at the homepage, you see the "Popular Tags" module. That shows a list of tags. There is no API call for that: the feature "tags" is implemented in the Vanilla application and if you look at /applications/vanilla/controllers/api you will see that there is no TagsApiController.
You would have to write that as a "MyTagsApiController" in a plugin by yourself.