problem using the dialout group

[Dave Stevens]

 I have a serial device connected to a uart that is connected to a usb 
port. I can use it ok if I sudo but that is not what is wanted. 
Instead I'd like to be able to use it as the logged in user, which 
will always be dave. I was told to try adding dave to the dialout 
group, so:

dave at dave-2021:~$ groups dave
dave : dave adm dialout fax cdrom sudo dip plugdev lpadmin sambashare

but this doesn't get me there. I'd like to copy incoming data to a 
file like this:

dave at dave-2021:~$ groups dave
dave : dave adm dialout fax cdrom sudo dip plugdev lpadmin sambashare

dave at dave-2021:~$ cp /dev/ttyUSB0 data.bin
cp: cannot open '/dev/ttyUSB0' for reading: Permission denied

dave at dave-2021:~$ stat /dev/ttyUSB0
  File: /dev/ttyUSB0
  Size: 0             Blocks: 0          IO Block: 4096   character 
special file
Device: 6h/6d    Inode: 526         Links: 1     Device type: bc,0
Access: (0660/crw-rw----)  Uid: (    0/    root)   Gid: (   20/ 
dialout)
Access: 2021-07-13 15:09:54.718052674 -0700
Modify: 2021-07-13 14:14:23.718052674 -0700
Change: 2021-07-13 14:14:23.718052674 -0700
 Birth: -

suggestions?

Dave