Here’s the Telegram desktop flatpak (available after you add the Flathub repo). This is default scaling with no additional tweaking to the screen.
The theme is Obsidian 2, which I got from gnome-look via github, i.e. not the default L5 theme.
I have no idea about the actual functioning of Telegram on the L5, but I would imagine it works fine. And you can scale the view down slightly if you want, of course.