With the deprecation of TLS 1.0 and 1.1 for PowerShell Gallery as of April 2020, the cmdlets Update-Module and Install-Module became broken. Thus, according to this article, some commands need to be executed to bring them alive again:

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12 
Install-Module PowerShellGet -RequiredVersion 2.2.4 -SkipPublisherCheck

If that still doesn't work, then run the following commands:

[Net.ServicePointManager]::SecurityProtocol = [Net.ServicePointManager]::SecurityProtocol -bor [Net.SecurityProtocolType]::Tls12
Register-PSRepository -Default -Verbose
Set-PSRepository -Name "PSGallery" -InstallationPolicy Trusted

TLS 1.0 and 1.1 were also recently deprecated at NuGet.org: But that was also previously announced.

Simply running Register-PSRepository -Default (without any additional parameters) worked for me. After that, the Gallery was successfully registered:

PS C:\Windows\system32> Get-PSRepository

Name                      InstallationPolicy   SourceLocation
----                      ------------------   --------------
PSGallery                 Untrusted            https://www.powershellgallery.com/api/v2/

My problem was the missing Proxy config

best solution from comments: https://www.zerrouki.com/working-behind-a-proxy/
thanks to @Vadzim

In PowerShell open Profile

PS> notepad $PROFILE

this opens Notepad with your profile setting, will be created of not exists.
then add:

[system.net.webrequest]::defaultwebproxy = new-object system.net.webproxy('http://webproxy.yourCompany.com:PORT')
[system.net.webrequest]::defaultwebproxy.credentials = [System.Net.CredentialCache]::DefaultNetworkCredentials
[system.net.webrequest]::defaultwebproxy.BypassProxyOnLocal = $true

somehow my local proxy is set but doesn't work. same problem later with Docker, =>

> PS> [Environment]::SetEnvironmentVariable("HTTP_PROXY", http://username:password@proxy:port/", [EnvironmentVariableTarget]::Machine)

then restart docker service