During the COVID lockout, I used my 2019 RC300h far less than I usually do. Three times in 2 months, the battery went dead.
I had to call Lexus support which, by the way, is very helpful and efficient.
The mechanics told me that this is a very common problem on Lexus hybrid cars, as they fitted with very limited battery power.
I never had this problem before and reported it to my Lexus dealer. He was not at all surprised as it seems to be a common problem. He did confirm that Lexus hybrids have a smaller battery. There is no real solution other than the dealer recommended that I start the car at least once a week, which I don't consider a very practical alternative.
My son-in-law had the same problem around this time on his IS300h.