The repository is added without problems, but when downloading, there are problems with TLS. The certificates are updated. A search of the forums did not provide a solution. Maybe there are some other debugging tools?
OS: Thinstation 6.2 (Crux)
ts_0800274dd952:~# flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo -v
F: Opening system flatpak installation at path /usr/var/lib/flatpak
F: Loading https://dl.flathub.org/repo/flathub.flatpakrepo using curl
F: Received 4040 bytes
F: Imported 1 GPG key to remote "flathub"
F: Clearing cached summaries for remote flathub
F: Fetching summary index file for remote ‘flathub’
F: Loading https://dl.flathub.org/repo/summary.idx using curl
F: Received 10001 bytes
F: Loading https://dl.flathub.org/repo/summaries/100cbcaf710555f3dc6e7c526a558708624dc5210da0eca67ebe4f434304deb3.idx.sig using curl
F: Received 592 bytes
F: Fetching indexed summary file 5069da7572a3ca7c9797314194998a4c760420adef4abd0577d6898a9d08429a.gz for remote ‘flathub’
F: Loading https://dl.flathub.org/repo/summaries/5069da7572a3ca7c9797314194998a4c760420adef4abd0577d6898a9d08429a.gz using curl
F: Received 1153431 bytes
ts_0800274dd952:~# flatpak install flathub org.cvfosammmm.Lemma -v -y
F: No installations directory in /usr/etc/flatpak/installations.d. Skipping
F: Opening system flatpak installation at path /usr/var/lib/flatpak
F: Opening user flatpak installation at path /root/.local/share/flatpak
Looking for matches…
F: Fetching summary index file for remote ‘flathub’
F: Loading https://dl.flathub.org/repo/summary.idx using curl
F: Received 10001 bytes
F: Loaded indexed summary file 5069da7572a3ca7c9797314194998a4c760420adef4abd0577d6898a9d08429a from cache for remote ‘flathub’
F: Transaction: install flathub:app/org.cvfosammmm.Lemma/x86_64/stable[*]
F: Looking for remote metadata updates for flathub
F: marking op install:app/org.cvfosammmm.Lemma/x86_64/stable resolved to 239b3108095d01222d152a8e01478fba806ce8d5c90c909b9893c93c36238c99
F: Installing dependency org.gnome.Platform/x86_64/45 of org.cvfosammmm.Lemma/x86_64/stable
Required runtime for org.cvfosammmm.Lemma/x86_64/stable (runtime/org.gnome.Platform/x86_64/45) found in remote flathub
F: Transaction: install/update flathub:runtime/org.gnome.Platform/x86_64/45[$old]
F: marking op install/update:runtime/org.gnome.Platform/x86_64/45 resolved to 57d12cbe72e28d786a210eced336f3ebcd99a229dd6dc1d55917cb9efb1ffa7d
F: Transaction: install/update flathub:runtime/org.gnome.Platform.Locale/x86_64/45[*]
F: Transaction: install/update flathub:runtime/org.freedesktop.Platform.GL.default/x86_64/23.08[$old]
F: Transaction: install/update flathub:runtime/org.freedesktop.Platform.GL.default/x86_64/23.08-extra[$old]
F: Transaction: install/update flathub:runtime/org.freedesktop.Platform.openh264/x86_64/2.2.0[$old]
F: marking op install/update:runtime/org.freedesktop.Platform.openh264/x86_64/2.2.0 resolved to bf24f23f3ba385f6e8c9215ed94d979db99814b0b614504a23a6d0751dc5f063
F: marking op install/update:runtime/org.freedesktop.Platform.GL.default/x86_64/23.08-extra resolved to 0f90faaea3e66a353bb667ee87b39eb49626d37d6117f37bba33b770b398b6c9
F: marking op install/update:runtime/org.freedesktop.Platform.GL.default/x86_64/23.08 resolved to 6896a1e84f623eba039b3a0eeabe21a16537f297460a3f3fcbcaab724cd97aaf
F: marking op install/update:runtime/org.gnome.Platform.Locale/x86_64/45 resolved to e4ddfd287490bc693a3b0b3900a544e11d8c7d6b226efd8fafee05f63cb9e204
F: Checking installation ‘system’ for EOL unused refs
F: Checking installation ‘system’ by checking for dependent refs in ‘user’
F: Checking installation ‘system’ for EOL unused refs
F: Checking installation ‘system’ by checking for dependent refs in ‘user’
org.cvfosammmm.Lemma permissions:
ipc fallback-x11 wayland x11 dri
1. org.freedesktop.Platform.GL.default 23.08 i flathub < 162.3 MB
2. org.freedesktop.Platform.GL.default 23.08-extra i flathub < 162.3 MB
3. org.freedesktop.Platform.openh264 2.2.0 i flathub < 944.3 kB
4. org.gnome.Platform.Locale 45 i flathub < 369.5 MB
5. org.gnome.Platform 45 i flathub < 375.1 MB
6. org.cvfosammmm.Lemma stable i flathub < 23.9 MB
Installing 1/6…
F: flatpak_dir_pull: Using commit 6896a1e84f623eba039b3a0eeabe21a16537f297460a3f3fcbcaab724cd97aaf for pull of ref runtime/org.freedesktop.Platform.GL.default/x86_64/23.08 from remote flathub
Installing 1/6… 0% 0 bytes/s
Warning: While pulling runtime/org.freedesktop.Platform.GL.default/x86_64/23.08 from remote flathub: Unacceptable TLS certificate
Installing 2/6…
F: flatpak_dir_pull: Using commit 0f90faaea3e66a353bb667ee87b39eb49626d37d6117f37bba33b770b398b6c9 for pull of ref runtime/org.freedesktop.Platform.GL.default/x86_64/23.08-extra from remote flathub
Installing 2/6… 0% 0 bytes/s
Warning: While pulling runtime/org.freedesktop.Platform.GL.default/x86_64/23.08-extra from remote flathub: Unacceptable TLS certificate
Installing 3/6…
F: flatpak_dir_pull: Using commit bf24f23f3ba385f6e8c9215ed94d979db99814b0b614504a23a6d0751dc5f063 for pull of ref runtime/org.freedesktop.Platform.openh264/x86_64/2.2.0 from remote flathub
Installing 3/6… 0% 0 bytes/s
Warning: While pulling runtime/org.freedesktop.Platform.openh264/x86_64/2.2.0 from remote flathub: Unacceptable TLS certificate
Installing 4/6…
F: flatpak_dir_pull: Using commit e4ddfd287490bc693a3b0b3900a544e11d8c7d6b226efd8fafee05f63cb9e204 for pull of ref runtime/org.gnome.Platform.Locale/x86_64/45 from remote flathub
Installing 4/6… 0% 0 bytes/s
Warning: While pulling runtime/org.gnome.Platform.Locale/x86_64/45 from remote flathub: Unacceptable TLS certificate
Installing 5/6…
F: flatpak_dir_pull: Using commit 57d12cbe72e28d786a210eced336f3ebcd99a229dd6dc1d55917cb9efb1ffa7d for pull of ref runtime/org.gnome.Platform/x86_64/45 from remote flathub
Installing 5/6… 0% 0 bytes/s
Error: While pulling runtime/org.gnome.Platform/x86_64/45 from remote flathub: Unacceptable TLS certificate
error: Failed to install org.gnome.Platform: While pulling runtime/org.gnome.Platform/x86_64/45 from remote flathub: Unacceptable TLS certificate