Why does Hextml displays "Save on server: never" in the status bar?You have to connect with your google account and get a premium account with at least a $5 tier. Then, the "server" text will transform into a link that you can click to access your personnal map.
If you can't (or don't want to) you can still use everything normally but you'll have to regulary save your maps on your own computer.
I usually enable the premium account after the first $5 payment has gone through. If you didn't know patreon has a weird payment system where you only get payed around the 3rd of each month.
Sharing the map with collaborative mode won't work unless you keep your browser tab open to replicate the changes on the server. You are the only one that can save at this specific URL. It doesn't work like Google docs where someone can access your docs if you're note here
Even if every editor has a premium account it won't wokrk: you will all save the map on the server but there will be many different copies at different URL.
Think of it this way: the collaboration link is only valid for as long as you have your browser tab open.