YouTube Playlist; SciX 2021 (suitable for high-school students)
Legal Open-Access Literature Papers:
Arxiv (physics, maths predominantly): Many fields (e.g. astronomy) have essentially all important papers here.
Chemrxiv (chemistry): Not as well established but worth checking.
Biorxiv (biology)
Ask the authors! (You will make their day and it is legal for them to share pdf directly with you).
Articulating skills helps students (& others) recognise and value their learning, promote their skills to future employers/ funders etc & plan for future growth.