Well, I must have been mistaken. I don’t actually know what the issue is, but Element doesn’t appear to be available from Flathub on the L5. Maybe they don’t have an ARM Linux version available via Flatpak?
I have seen in the Matrix chatrooms that Kyle has used the web version in the L5 browser, but I think some things do not scale properly there.
You could also consider trying this (from the Element website):
sudo apt install -y wget apt-transport-https
sudo wget -O /usr/share/keyrings/riot-im-archive-keyring.gpg https://packages.riot.im/debian/riot-im-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/riot-im-archive-keyring.gpg] https://packages.riot.im/debian/ default main" | sudo tee /etc/apt/sources.list.d/riot-im.list
sudo apt update
sudo apt install element-desktop