Setting variable QT_SCALE_FACTOR=0.8 at Exec line in telegramdektop.desktop file (now it’s looks like Exec=QT_SCALE_FACTOR=0.8 telegram-desktop – %u) helped me. If that doesn’t help, you can try to choose other value for QT_SCALE_FACTOR variable.
Setting variable QT_SCALE_FACTOR=0.8 at Exec line in telegramdektop.desktop file (now it’s looks like Exec=QT_SCALE_FACTOR=0.8 telegram-desktop – %u) helped me. If that doesn’t help, you can try to choose other value for QT_SCALE_FACTOR variable.