Nonsetrile compounding, like you'd do from the peptide sites is only safe for immediate use, and semaglutide is not that way. You mix up a vial and use it for a month or so.
Can you do it? Sure. Are you going to get an infection from it? Probably not. Is it riskier than having a compounding pharmacy doing it the right way? Absolutely, and in a meaningful amount of risk. The type of infections you get from contaminated injections are not something you want to deal with