A shell script to get into the shell of a flatpak.
Let's see what comes up on my system for freedesktop:
$ enterflatpak freedesk
No running instance found for flatpak: freedesk
1) org.freedesktop.LinuxAudio.Plugins.Calf,25.08,x86_64,system 15) org.freedesktop.Platform.GL.default,24.08,x86_64,user
2) org.freedesktop.LinuxAudio.Plugins.LSP,25.08,x86_64,system 16) org.freedesktop.Platform.GL.default,25.08,aarch64,user
3) org.freedesktop.LinuxAudio.Plugins.MDA,25.08,x86_64,system 17) org.freedesktop.Platform.GL.default,25.08-extra,aarch64,user
4) org.freedesktop.LinuxAudio.Plugins.ZamPlugins,25.08,x86_64,system 18) org.freedesktop.Platform.GL.default,25.08-extra,x86_64,system
5) org.freedesktop.Platform,24.08,x86_64,system 19) org.freedesktop.Platform.GL.default,25.08-extra,x86_64,user
6) org.freedesktop.Platform,24.08,x86_64,user 20) org.freedesktop.Platform.GL.default,25.08,x86_64,system
7) org.freedesktop.Platform,25.08,x86_64,system 21) org.freedesktop.Platform.GL.default,25.08,x86_64,user
8) org.freedesktop.Platform,25.08,x86_64,user 22) org.freedesktop.Platform.openh264,2.5.1,x86_64,system
9) org.freedesktop.Platform.codecs-extra,25.08-extra,aarch64,user 23) org.freedesktop.Platform.openh264,2.5.1,x86_64,user
10) org.freedesktop.Platform.codecs-extra,25.08-extra,x86_64,system 24) org.freedesktop.Sdk,24.08,x86_64,system
11) org.freedesktop.Platform.codecs-extra,25.08-extra,x86_64,user 25) org.freedesktop.Sdk,24.08,x86_64,user
12) org.freedesktop.Platform.GL.default,24.08extra,x86_64,system 26) org.freedesktop.Sdk,25.08,aarch64,user
13) org.freedesktop.Platform.GL.default,24.08extra,x86_64,user 27) org.freedesktop.Sdk,25.08,x86_64,system
14) org.freedesktop.Platform.GL.default,24.08,x86_64,system 28) org.freedesktop.Sdk,25.08,x86_64,user
Select flatpak to enter or q to quit: q
Note that the output includes multiple choices. What makes the list unique is the application name, its branch, the architecture, and whether or not installed on the system vs the user.
In any event, the output is a bit much, let's narrow it down to the Sdk:
$ enterflatpak freedesktop.Sdk
No running instance found for flatpak: freedesktop.Sdk
1) org.freedesktop.Sdk,24.08,x86_64,system 3) org.freedesktop.Sdk,25.08,aarch64,user 5) org.freedesktop.Sdk,25.08,x86_64,user
2) org.freedesktop.Sdk,24.08,x86_64,user 4) org.freedesktop.Sdk,25.08,x86_64,system
Select flatpak to enter or q to quit: 5
Entering flatpak org.freedesktop.Sdk
(Sdk-freedesktop-sdk-25.08.7) $
So, now at a shell prompt within the flatpak. In this example, an instance wasn't running, so the script started it.