Ubuntu 23.10下Snap启动缓慢问题求助：xdg-document-portal因缺失FUSE_3.12无法启动

最近我碰到了一个头疼的问题：所有Snap应用启动都特别慢。用--trace-exec参数运行Snap程序时，日志开头总会弹出这条警告：

2024/01/05 18:13:22.350176 cmd_run.go:1055: WARNING: cannot start document portal: Failed to activate service 'org.freedesktop.portal.Documents': timed out (service_start_timeout=120000ms)

看起来问题和xdg-desktop-portal有关，我查到有人通过修复.local/share/flatpak目录的权限解决过类似问题，但我系统里根本没有这个目录。

进一步排查后，我发现是xdg-document-portal服务启动失败了，执行systemctl --user status xdg-document-portal.service得到的结果如下：

× xdg-document-portal.service - flatpak document portal service
Loaded: loaded (/usr/lib/systemd/user/xdg-document-portal.service; static)
Active: failed (Result: exit-code) since Fri 2024-01-05 18:19:54 GMT; 1s ago
Process: 9581 ExecStart=/usr/libexec/xdg-document-portal (code=exited, status=1/FAILURE)
Main PID: 9581 (code=exited, status=1/FAILURE)
CPU: 2ms

Jan 05 18:19:54 CSLLAP- systemd[4067]: Starting xdg-document-portal.service - flatpak document portal service...
Jan 05 18:19:54 CSLLAP- xdg-document-portal[9581]: /usr/libexec/xdg-document-portal: /usr/local/lib/x86_64-linux-gnu/libfuse3.so.3: version `FUSE_3.12' not found (required by /usr/libexec/xdg-document-portal)
Jan 05 18:19:54 CSLLAP- systemd[4067]: xdg-document-portal.service: Main process exited, code=exited, status=1/FAILURE
Jan 05 18:19:54 CSLLAP- systemd[4067]: xdg-document-portal.service: Failed with result 'exit-code'.
Jan 05 18:19:54 CSLLAP- systemd[4067]: Failed to start xdg-document-portal.service - flatpak document portal service.

核心错误就是这条：

Jan 05 18:19:54 CSLLAP- xdg-document-portal[9581]: /usr/libexec/xdg-document-portal: /usr/local/lib/x86_64-linux-gnu/libfuse3.so.3: version `FUSE_3.12' not found (required by /usr/libexec/xdg-document-portal)

我不太懂FUSE是什么，但我系统里明明已经装了更高版本的libfuse3：

$ sudo apt install libfuse3-dev
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
libfuse3-dev is already the newest version (3.14.0-4).
0 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade.

现在我有几个问题想请教大家：

• xdg-document-portal真的必须依赖FUSE 3.12版本吗？
• 除了手动安装FUSE 3.12之外，还有其他更稳妥的修复方法吗？
• 有没有办法让Snap应用不依赖这个服务就能正常运行？

我的系统信息：

[~]$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 23.10
Release:    23.10
Codename:   mantic

[~]$ uname -a
Linux CSLLAP- 6.5.0-14-generic #14-Ubuntu SMP PREEMPT_DYNAMIC Tue Nov 14 14:59:49 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

编辑补充：目前我找到一个临时 workaround，就是按照FUSE仓库的说明手动安装3.12版本，但我还是想搞清楚背后的原因到底是什么。

备注：内容来源于stack exchange，提问作者Nobilis