Focus on a Consistent, Predictable, and Sustainable Cadence
Scrum is not very prescriptive about when to schedule the start or end of each Sprint, but the common practice is to only schedule framework events and planned work during standard working days. If the team doesn't usually work on the weekends, then don't base the project plan on doing work or holding events like Sprint Planning on the weekends outside of truly exceptional circumstances.
More importantly, a core tenet of agile frameworks like Scrum is to maintain a predictable cadence for events, meetings, and deliverables. So, if your first Sprint starts on Monday, then every Sprint should generally start on a Monday. Likewise, if your first Sprint ends on a Friday, then every Sprint should end on a Friday.
Of course, holidays, staffing shortages due to the pandemic, or other force majeure events can force the team to adapt the schedule when necessary, but consistency and predictability for both the team and the stakeholders remains the key objective. Starting or ending your Sprints on a different day of the week each Sprint would not meet that goal.
The related question of whether weekends within each Sprint's time box are included in the Sprint or not is a separate topic. That has to be answered by the team based on how they work together and as individuals, how they manage their hours, how they organize their work, how self-managing they are, whether your team has routine coverage on the weekends, and a lot of other considerations not included in your original post. If a high-performing team wants to work four-day work weeks, or spread out the work to include weekends, that's really up to them so long as the framework events are held at predictable days and times, and as long as the process is working for both the team and the stakeholders.
Some of the best engineers I know do their best work at 2:00 AM. From a framework point of view, as long as they're available for the Daily Scrum, Sprint Planning, and so forth it's none of my business how the team self-organizes so long as it's consistent and sustainable for the duration of the project.