Yep I’m on 26.4 Beta 1
And yes, brightness does increase when I press ctrl+opt+cmd+shift + M
I just tried and can reproduce, capslock+m doesn’t trigger brightness, but cmd+ctrl+shift+opt+m does. My other hyperkey bindings seem to work fine, and if I set capslock+m to volume-up it also works 
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Ah, then I think I know what causes this (it is pretty specific to the brightness actions).
I will probably be able to solve it but I'll need to do some tests.
//edit I believe this has always been like this because the brightness keys do not work while ctrl is pressed (they work, but they then change the brightness of the external display)
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Haha yep, can confirm volume works for me too
Thanks Andreas!
Another confirmation for the Hyperkey fix in latest alpha.
Thanks so much @Andreas_Hegenberg.
I can confirm that the Hyper Key does not work as expected. However, some strange bugs have popped up, and I cannot for the life of me figure out why they are occurring. It is true that when I press Caps Lock in a BTT input box, it registers as it should with all four modifiers. It also works correctly when I use my keyboard commands with the Hyper Key in combination with any letter, number, etc. However, the issue is that for some reason, when Caps Lock (Hyper Key) is double-clicked—or clicked after a previous click, perhaps leaving a key stuck or not fully released—it triggers Right Control + Right Control key sequence. I have that combination set to the Hyper Key's AI feature (Bring Your Own Key/API). It's very strange. I've been racking my brain and can't figure out why it would be doing that. Does anyone have any ideas?
That is most likely due to how the workaround works. You can use this command to switch to an alternate "workaround mode" which should prevent issues with right-ctrl key sequences:
osascript -e 'tell application "BetterTouchTool" to set_user_defaults key "BTTHyperKeyUseAlternateMode" numberValue 1'
Possibly I'll make that the default mode
Apple resolved the issue in 26.4 beta 3, so I will disable the workaround again with the next alpha!