There's a new cello camp for adult amateur cello players by the founder of the Summerkeys cello workshop in Midcoast Maine last 2 weeks of August(1 week workshops).

Here's a description from the website(www.midcoastcelloworkshop.com)
Come develop your playing!
Learn in a supportive friendly atmosphere

25 years ago cellist Peter Lewy started the Cello Workshop at The SummerKeys Music Festival dedicated to helping amateur adult cello players improve their skills. It has expanded enormously and met every year until Covid. The festival is not going to resume this year so he is going to do two 1 week sessions in the Midcoast region of Maine as he did last year. Last year the workshop was Virtual but this year there will be virtual and in person options.
The workshop offers five private lessons, use of private practice studio two hours daily, daily group classes, ensemble work, 2 “master class” style instruction classes, and an end of week performance opportunity. An accompanist is available.
The Cello Workshop at SummerKeys opened its doors in 1995, utilizing the same basic precept as the original piano program, an intensive practice/study vacation for busy adults who rarely have this kind of time to devote to their instrument during the rest of the year in a breathtakingly beautiful setting.
Each day begins with an hour-long group class for all participants at 9 AM.
Evening Activities include a Faculty Concert (Wednesday) and a performance opportunity for those who wish to improve their performance skills. There is no audition and no minimum skill level, the premise is: “Come as you are to enjoy the study, the work and the beauty of our historic fishing village”. Absolute beginners with no previous instruction to professionals are welcome.
We all learn from each other!