Error in the certificate verification WSL2

From my personal computer (Win 11) where I have installed WSL2 with Ubuntu 20.04, I am having some difficulties installing programs.

I tried to install OpenFoam and Geogebra and with both I get an error related to certificates.

Could anyone help me understand why and how to solve?

When installing GEOGEBRA with:

sudo apt-add-repository -u 'deb http://www.geogebra.net/linux/ stable main'

I get the error:

...Err:17 https://sourceforge.net/projects/openfoam/files/repos/deb focal Release  Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate.  Could not handshake: Error in the certificate verification. [IP: 204.68.111.105 443]Get:20 http://archive.ubuntu.com/ubuntu focal-updates/universe Translation-en [207 kB]Get:21 http://archive.ubuntu.com/ubuntu focal-updates/universe amd64 c-n-f Metadata [20.7 kB]Reading package lists... DoneW: GPG error: http://www.geogebra.net/linux stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C072A32983A736CFE: The repository 'http://www.geogebra.net/linux stable InRelease' is not signed.N: Updating from such a repository can't be done securely, and is therefore disabled by default.N: See apt-secure(8) manpage for repository creation and user configuration details.E: The repository 'https://dl.openfoam.com/repos/deb focal Release' does not have a Release file.N: Updating from such a repository can't be done securely, and is therefore disabled by default.N: See apt-secure(8) manpage for repository creation and user configuration details.

With OpenFOAM:

Add the repository

curl https://dl.openfoam.com/add-debian-repo.sh | sudo bash  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                 Dload  Upload   Total   Spent    Left  Speed100  3862  100  3862    0     0  11392      0 --:--:-- --:--:-- --:--:-- 11358Detected distribution code-name: focalOverwrote /etc/apt/sources.list.d/openfoam.listImporting openfoam gpg key... doneOverwrote /etc/apt/trusted.gpg.d/openfoam.gpgRunning apt-get update... doneThe repository is setup! You can now install packages.

Install preferred package:

sudo apt-get install openfoam2112-defaultReading package lists... DoneBuilding dependency treeReading state information... DoneE: Unable to locate package openfoam2112-default

At this linkthey proposed this solution:

sudo apt install ca-certificates

And for geogebra I found this proposed solution.

But before proceeding I would like to understand the problem better.

Can someone help me understand it better please?