There are a few things to consider before enrolling your high schooler in Geometry in the summer. Does your teen like Math? Is Math a strong subject? How fast can your teen grasp mathematical concepts?
Summer School classes try to cover 1 year worth of work in about 6 weeks (depending on where your high schooler takes Geometry). Also, having a strong grasp of Geometry is important for the SAT. (Some colleges and universities are waiving standardized testing or are test-optional) until 2024. So, this may not be a factor for you.
Last and most importantly, is your high schooler spatial? (Is he/she good at putting puzzles together, drawing, interpreting graphs and charts, playing chess or building with Legos?) If so he/she is spatial and Geometry may not be as challenging. If your high schooler is not spatial, it is still possible to be successful in Geometry during the summer, but it will require more time, energy, effort and discipline.
Depending on where your child stands on theses questions, and specifically the spatial question, will help you determine if a quick accelerated summer course is best or a year long course with more time to learn the skills and concepts.
Finally, make sure you check with the school to get permission before enrolling in any summer course. Geometry is one of the few Math classes schools will allow students to take during the summer.