• https://itsfoss.com/downgrade-flatpak-packages/

List installed Flatpak apps

flatpak list --app

Name                    Application ID                        Version                      Branch          Origin           Installation
Flatseal                com.github.tchx84.Flatseal            2.0.1                        stable          flathub          system
draw.io                 com.jgraph.drawio.desktop             21.2.8                       stable          flathub          system
Microsoft Teams         com.microsoft.Teams                   1.5.00.23861                 stable          flathub          system
OBS Studio              com.obsproject.Studio                 29.1.2                       stable          flathub          system
Spotify                 com.spotify.Client                    1.2.11.916.geb595a67         stable          flathub          system
Filius                  de.lernsoftware_filius.Filius         1.14.1                       stable          flathub          system
FreeTube                io.freetubeapp.FreeTube               0.18.0 Beta                  stable          flathub          system
Signal Desktop          org.signal.Signal                     6.17.1                       stable          flathub          system
Tenacity                org.tenacityaudio.Tenacity                                         nightly         tenacity         system

List available package versions

flatpak remote-info --log flathub <Application ID>

flatpak remote-info --log flathub org.signal.Signal
        ID: org.signal.Signal
       Ref: app/org.signal.Signal/x86_64/stable
      Arch: x86_64
    Branch: stable
Collection: org.flathub.Stable
  Download: 155.9 MB
 Installed: 434.6 MB
   Runtime: org.freedesktop.Platform/x86_64/22.08
       Sdk: org.freedesktop.Sdk/x86_64/22.08

    Commit: 509acbd56b3b348dad12c368a5c401f631b01316a6dd1b27606f5cf2af906d05
    Parent: 26cd2da3abcdb75999eb2de686a9528ec1ec0c2785551c57ab670e8e2796ed74
   Subject: fix license (#455) (1368ef27)
      Date: 2023-05-30 12:30:32 +0000
   History: 

    Commit: 26cd2da3abcdb75999eb2de686a9528ec1ec0c2785551c57ab670e8e2796ed74
   Subject: Update signal-desktop.deb to 6.19.0 (998721ff)
      Date: 2023-05-26 19:00:36 +0000

    Commit: 79ac656c6e3892f83b4e71f7d669dd20d26a794d65a997e470257d259b2c1dba
   Subject: Update signal-desktop.deb to 6.18.1 (29cd7747)
      Date: 2023-05-22 23:44:55 +0000

    Commit: c7cf7d75364a78f7c92804de9b43d65d8e00539f6dad62bc30ab86898ac6129b
   Subject: Update signal-desktop.deb to 6.18.0 (29da33c9)
      Date: 2023-05-18 21:51:46 +0000

    Commit: d4310eb0b784cbcf9642f3ca3f050a4c79a5423b4e06f2cebdda52acf0426776
   Subject: Update signal-desktop.deb to 6.17.1 (d049d73f)
      Date: 2023-05-11 21:44:48 +0000
      
   ...
   ...

Install specific versions commit

flatpak update --commit=c7cf7d75364a78f7c92804de9b43d65d8e00539f6dad62bc30ab86898ac6129b org.signal.Signal

Mask package to prevent updates

flatpak mask org.signal.Signal

Remove masking

flatpak mask --remove org.signal.Signal

~~DISCUSSION~~