Those in the linked list are mostly paid or funded “camp” like programs, not internships as your post asks about.
My DS did go to the WPI frontiers one and it was great, but went knowing this was not something that would boost admissions chances, just exploring possible majors and WPI.
If they are looking for job experience in STEM, there may be something close to home that is still available. Cities and counties often fund paid youth job opportunities and there are a variety of STEM related careers. Those applications are being accepted now in many places - I know in Boston, MA and Charleston, SC. You must be a resident of that area usually. Some school districts offer this as well.
Helping with or working at STEM summer camps locally is also a great opportunity. There is usually training and it gets them out of their comfort zone. They are all still hiring.
They will need a resume if applying for jobs and internships. They may need help with that.
They could also take a college level class at a local college. Look at the summer catalogs.