corbu1

Are you running DCS on Open Beta? Only with OB you can already use the 114L.
If you are on DCS stable you have to wait until stable version gets updatet.

If you mean the frequency swap button on the EUFD this us actually since May OB patch update not working. His was noted by the Def‘s as necessary WIP for doing further development for the comm systems.

You have RLWR active on ASE - UTIL page?
Did you also set RLWR audio on comm panel on right side in cockpit?
missile warning is CMWS

Elgato Streamdeck definitlly works with the AH64D. I use several of them (see may signature). 
Besides the the link @AndyJWestalready posted there are a few profiles under user files. There‘s also a nice icon library for creating your own profiles for the AH64D.

Deicing systems are actually wip.
Therefore the these functions are actually deactivated till deicing is implemented.

It was announced recently for a later release in 2023, but not in 2022 or even this actual OB.

With new OB getting the hold modes in cruise flight works as before.
In Hover I had to press FTR and get in a trimmed state then hover hold and altitude hold can be engaged…..curious if this was changed or it is just me thinking it changed. I trimmed anyway before engaging the hold modes in hover before, but now I felt it‘s necessary to engage them.
I noticed the SAS beeping sound events have changed with activating/ deactivating the hold modes as well.
Altitude hold disengages on it‘s own when stable parameters get lost?
Edit:
Altitude hold disengage parameters are described in DCS AH64D manual. Actual OB looks good for me n this aspect.

The PERF page is actually under overhaul by the devs and therefore deactivated….