I just downloaded the KeyboardCleanTool and notice that while in the locked mode, you can still double-press the Command key to open/close the Siri text input field. With the keyboard otherwise disabled, you can't actually type into the field, but you can still at least toggle it on/off.
For reference I'm on an MBP 2021 14-inch with an M1 Pro chip and running Sequoia 15.2 (24C101)
this is a limitation of the simple approach keyboardcleantool uses - modifier keys can not be blocked using that.
Maybe I’ll update the tool at some point to add a way to block them as well. However it is currently not super high priority
Understood, and I figured you probably don't give much time to it since it's a free utility. I just wanted to at least mention it. And why Apple would reject the utility as not being useful is anyone's guess. Personally, I get pretty annoyed with trying to clean off my keyboard only to accidentally mess up the screen brightness or volume, etc. This will save my sanity. 
Thanks.
@JessePeden I assume you also own BTT. Have you tried if it works better when BTT blocks the keyboard?
Otherwise you could set up in blocked mode double-press cmd does nothing, at least I think so 
