I try to run it on two devices:
MacBook Pro 16" 2019, 2.4Ghz 8-Core Intel Core i9, 64GB RAM with BigSur 11.2.3.
iMac Pro 27" 2017, 3GHz Intel Xeon W, 64GB RAM with BigSur 11.2.3.
BUT: I just started CCleaner to produce an error report but this time let it hang for say 3-5 min. At the end it came up as planned! Might it be that for a first start the app needs several minutes to establish all the necessary?