Is moving to a competitor company for a higher salary, by utilizing the experience and relationships gained in the previous company, considered a betrayal, and what are the standards of fair competition that please Allah?

If the contract between you and your company has expired, or if the company has agreed to terminate the contract before its expiry, then there is no blame upon you for moving to another company to obtain a higher salary or lighter work. This is not treachery or an infringement on the rights of others, even if the new company is a competitor to the previous one. Honorable competition is based on truthfulness, proficiency, and the absence of monopoly.