@atripp It does not work.

I have added a source successfully

nuget sources add -Name "Lighthouse" -source https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json -u feeduser -p ??????????????????????? -StorePasswordInClearText
Package source with Name: Lighthouse added successfully.

nuget push test.nupkg -source https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json
MSBuild auto-detection: using msbuild version '15.0' from '/usr/local/Cellar/mono/6.12.0.182/lib/mono/msbuild/15.0/bin'.
Using credentials from config. UserName: feeduser
The remote server indicated that the previous request was forbidden. Please provide credentials for: https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json
UserName:

Even entering the api key in the command line does not work
nuget push /Volumes/c$/Nuget/Packages/lighthouse.lh3.frontend/2.0.68/lighthouse.lh3.frontend.2.0.68.nupkg -source https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json -ApiKey ??????????????????
MSBuild auto-detection: using msbuild version '15.0' from '/usr/local/Cellar/mono/6.12.0.182/lib/mono/msbuild/15.0/bin'.
Using credentials from config. UserName: feeduser
The remote server indicated that the previous request was forbidden. Please provide credentials for: https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json
UserName:

Here the output from docker logs
nfo: Microsoft.AspNetCore.Hosting.Diagnostics[1]
Request starting HTTP/1.1 GET https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json - -
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
Request finished HTTP/1.1 GET https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json - - - 401 84 - 7.9011ms
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
Request starting HTTP/1.1 GET https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json - -
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
Request finished HTTP/1.1 GET https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json - - - 403 17 - 25.3999ms
info: Microsoft.AspNetCore.Hosting.Diagnostics[1]
Request starting HTTP/1.1 GET https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json - -
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
Request finished HTTP/1.1 GET https://nugetsrv.lighthouse.gr:8443/nuget/lighthouse/v3/index.json - - - 403 17 - 24.7868ms

@atripp RE:" Are you trying to use Docker images, for example?"
Not yet. I have created a nuget feed.
The api key works fine in the nuget push command but not in the nuget list

I'm currently evaluating the latest docker (proget.inedo.com/productimages/inedo/proget:23.0.20) and the api key seems not work.
Although the user can be authenticated with the username and password, using the api key as password is not working