Can't Add Repository "Could not find a distribution template for elementary/hera"

I wanted to add Inkscape repository to download Inkscape 1.0 which is not available in the default elementary repository. Before I’ve ever done sudo add-apt-repository and it just worked fine. Only recently when I tried to add Krita’s repo it didn’t work and have some aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for elementary/hera so I did a workaround by manually adding the link to synaptic. But the problem is, ppa for Inkscape is not a http but ppa: and when I tried to manually do the same it couldn’t find the repository.

Here’s the full result of sudo add-apt-repository

sudo add-apt-repository ppa:inkscape.dev/stable

Traceback (most recent call last):
File "/usr/bin/add-apt-repository", line 107, in
sp = SoftwareProperties(options=options)
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 117, in init
self.reload_sourceslist()
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 612, in reload_sourceslist
self.distro.get_sources(self.sourceslist)
File "/usr/lib/python3/dist-packages/aptsources/distro.py", line 93, in get_sources
(self.id, self.codename))

aptsources.distro.NoDistroTemplateException: Error: could not find a distribution template for elementary/hera

There’s a similar question here but I guess it only works for Freya.

edit:

Here’s the output of tail /etc/lsb-release

DISTRIB_ID=elementary
DISTRIB_RELEASE=5.1.3
DISTRIB_CODENAME=hera
DISTRIB_DESCRIPTION="elementary OS 5.1.3 Hera"