As has been recommended, invest some time reading the official Scrum Guide (there are not multiple).
Scrum does NOT require or even recommend releasing the software at any particular interval. It only mandates that work made "Done" within the Sprint timebox should be "potentially releasable" should the Product Owner decide to do so.
A Sprint is
a time-box of one month or less during which a “Done”, useable, and potentially releasable product Increment is created.
The choice of Sprint length should always be a business decision and never a technical one.
To better manage your Sprints, allow the Development Team to plan its own work and build its own forecasts.
Development Teams are structured and empowered by the organization to organize and manage their own work.
The whole development team should plan (read: not just a PM or a "lead" developer) the work it will undertake in a Sprint and must plan for conditions such as developer vacation, technical dependencies, etc. Doing this will increase the likelihood of realistic forecasts, better planning, and more trust with clients.
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