Hi, @lauccode!
The reason the aforementioned plugins are archived is that @andreyorst stopped using Kakoune and, understandably, lose interest in maintaining them.
The good news is that, specif for fzf.kak there are two alternatives that come to my mind.
First, if you do want to stay with the fzf program, you can take a look at popup.kak by @enricozb (an amazing plugin by the way; congrats, Enrico!). By using it, filtering files with fzf is just a matter of calling
popup --title open --kak-script %{edit %opt{popup_output}} -- fzf
The other alternative is a plugin called Peneira, developed by me. It’s a general purpose fuzzy finder you can use for many use cases: filtering files, or lines inside a file, or jump to symbols in a source code… you can even easily define your own custom filters, like @mbauhardt did here.
The advantage of both alternatives, compared to fzf.kak is that you don’t need to run Kakoune inside a tmux session. They are very tightly integrated in Kakoune’s UI.
I hope any one of them can be useful for you.