Consider moving this step to after "Create Issues". After the issues are created and defined, there should be a step for assigning the issues to devs and reviewing as a group to confirm that everything is clearly defined, before moving on to Phase 2. The GitHub views that you're describing here seem to me to be part of that step...how to visualize and review the scope of work for the release as a team to ensure balanced workload.

Explain what the Milestone represents

Before diving into how GitHub is used during the Planning Phase, please add a brief description of the purpose of this phase, what needs to be accomplished and the desired outputs or end state of the first week. Same goes for the other phases as well.

This is a nice visualization. We'll want to consider if there are weeks that should be skipped. For example, holiday weeks where there are only 3 work days or where staff are likely to be out of office. We can revisit this as we decide how and when to launch this cycle.

The doc is nicely structured by the 3 Phases, though the introduction is missing a clear explanation of how the phases map to the weeks. For increased clarity, in this "Cycle Length" section, I suggest adding the names of the phases here alongside the weeks, and in the table below.

Which week does merging take place? It's mentioned in Step 5 of the Development Phase above as well...which is confusing. Merging is a separate step from communications...currently it's not clear when the merging happens. Suggest making merging its own step to increase clarity, since it's an important part of the release process.

Project management is a very vague title. In reality, this entire SOP is a project management tool. Can you give this step a more specific title? These steps seem to describe closing out the GitHub items to prepare and reset for the next cycle...so maybe something like "cycle wrap-up" or "cycle close-out"??

This is a bit confusing. I'd suggest that unfinished issues should go into the backlog instead -- and then during the first week of the new cycle, the process is restarted to select which issues will go into that cycle.

Is the reviewing step part of the 2 week dev period? If so, this should be stated clearly in the initial description of the Development Phase. Reviewing is an additional task on top of development, and currently this reads as a bit of a hidden surprise at the end of this section. It's important to call it out up front.

What is the process for determining who will review (if only 1 reviewer is needed)?

Avoid using "I" so that this is written as a document that reflects processes used by the entire team. Suggest either using "we" or 3rd person.