Do I put a comma after “but”or before “but”

I have no explanation, but I have this example. :)

Portfolios as a means of developing and assessing writing skills1

Abstract

English: Writing portfolios can serve various purposes: They can be used both as a tool for supporting and facilitating learners’ individual learning processes and as an assessment tool, which rather focuses on learning outcomes and achievements. Through the use of portfolios, improved learning processes, a more holistic approach to assessing writing skills, and, ultimately, better learning outcomes are expected

hope this is helpful for you