I'm not sure if this is still being worked on however adding libsoup-2.4 to the flatpak manifest fixes the flatpak build errors here:

  - name: libsoup-2.4
    buildsystem: meson
    sources:
      - type: git
        url: https://gitlab.gnome.org/GNOME/libsoup.git
        tag: '2.74.3'
    config-opts:
      - '-Dvapi=enabled'
  - name: code
    buildsystem: meson
    config-opts:
     - '-Dhave_pkexec=false'
    sources:
      - type: dir
        path: .

The Flatpak version of Code needs a lot of work as I recall to make it fully functional. Several things do not currently work in a sandbox.

IIRC, the issues with the flatpak version compared with the host one was the empty "Open In" menu, not having the real path to files to disambiguate the labels, and a libgit2-glib code/vapi missmatch.

for the "Open In" menu, a solution using the OpenURI portal was rejected in favor of using a future "Share" portal (see: #1162 (comment)).

for the libgit2-glib issue, we could fix it with a patch in the manifest, or in code itself (see: #1091).

for the file paths, there's nothing we can do really as it's a limitation from using portals.

So, i would say it pretty complete already.

There is also possible problems around development workflows like mine where you are using Flatpak Code and non-Flatpak Terminal (and occasionally non-Flatpak Files). These could go away if and when Code becomes a completely self contained IDE. I'll try to give Flatpak some more attention.

The tab disambiguation problem could maybe be fixed by using the project name as the root of the path.