on Oracle Linux delete CDB not free memory

SO : OracleLinux 8.7 - 2 nodes

Oracle Enterprise edition 19c (19.18.0.0) RAC environment 2 nodes ASM storage

I deleted a CDB with 320GB of SGA memory with dbca utility. At the end of the operation, without errors, the server memory is not freed. Once both nodes have been rebooted, the memory remains occupied.

[root@~]# free -lm

              total       used       free     shared buff/cache  available

Mem:        515368     428842      79705       2375       6820      79975

Low:        515368     435663      79705

High:            0          0          0

Swap:        16383          0      16383

[root@oraracmo01 ~]# ipcs -m

------ Shared Memory Segments --------

key       shmid     owner     perms     bytes     nattch    status

0x6001e1c8 0         grid      600       73728     49

0x50b73928 1         grid      600       12288     21

0x00000000 2         oracle    600       37748736  407

0x00000000 3         oracle    600       66706210816 407

0x00000000 4         oracle    600       98566144  407

0xf6e4ff20 5         oracle    600       81920     407

Why? there is the problem?