external drive - can't write to it
I have a brand new 16" MacBook Pro that came with Monterey 12.0.1
I want to create a directory on an external drive (that I have used for years on my older Catalina MacBook Pros) but I can't. Sharing and Permissions show brianthomas (Me) - Read & Write, Staff - Read Only and everyone - Read Only. Probably something to do with this...? I unlock the padlock and try to change the Read Only to Read & Write for the Staff and Everyone. "Operation can't be completed...don't have necessary permissions."
I investigate and apparently I have to go into Recovery mode and in Terminal I should run CSRUTIL DISABLE to resolve this. Eventually I find that for M1 Macs I get into Recovery Mode by keeping my finger on the Power button. I run the CSRUTIL command, I reply Y to the question, restart normally but I still can't change the Staff and Everyone users for the external drive to Read & Write. Should I even have to do this?
Surely connecting and using a simple external drive has to be easier that this? Please, please where am I going wrong?
MacBook Pro (2020 and later)