Not passing an entity ID to a service to target all entities is deprecated. Use instead: entity_id: "all"
Which is a breaking change but I have no idea how it is being caused.
EDIT:
I think I need to be clear that I discovered this during testing and for that I was using Arm Home as I have that set to arm immediately. Arm Home is something I have no intention currently of implementing for real so I have no other code that refers to Arming Home so I find it hard to understand how this error is being caused.
Targetting all entities in a domain by not sending an entity_id to a service is now deprecated. Instead, send entity_id: all if you want to target all. The old method will work for a couple of releases more, but will print a warning. Please migrate. (@balloob - #19006) (breaking change)
Do you have any automation or scripts that run when arming the Manual Alarm Control Panel?
Thanks yes I read that breaking change and no, as far as I can tell I have no automations or scripts that run when arming. I would never knowingly omit the entity_id anyway as I didn’t even know you could!!
I will of course be going through my code with a fine tooth comb to find this if it is my problem but I really would be surprised to find it.
It would be nice if the error message was a little more informative but that is a common complaint I have with HA!!
Not specifically but as I said I was only doing some initial testing, I have rewritten a lot of what I originally had but not fully experimented to see what happens.
Sorry, not a lot of help.
Does this mean you have something similar?