You can choose one cloud provider first (possibly from AWS/GCP/Azure).
Since you are from .Net IMO Azure might fit the best but you can double check from the market demand.
Nowadays every cloud provider is providing some free credits to use their cloud to learn about their services.
Some are also providing learning materials including hands-on labs.
And if they aren't providing then you can learn from YouTube channels like Technical Guftagu or Nana Jenashia.
However please keep in mind that you are focusing first on clearing some basics about Linux and Networking before starting your actual cloud learning journey.
Wishing you the best!