Ah yeah, spotted it straight away on Google Maps!
What was the reason behind removing only a part of it, rather than all?
Likely just a work in progress
Perhaps Mr Sunak in 2023 had something to do with the work not progressing
The previous plan (currently paused) was to demolish some more of the west side of the station to enable a bigger phase 1 build of the HS2 station (~13-15m at the southern end).
The Parcel Deck roof has been stripped back roughly to the centreline of the P14-P15 island where major support at the platform level below is.
The plan was to:
1) lift the "Middle Siding 2" track, very slightly realign the "Middle Siding 1" track (including approach in throat), build a new temporary platform (new 16) beside "Middle Siding 1" on the current "Middle siding 2" track alignment. This needs some more parcel deck removal due to where the supports are at the country end (hence the cutting back of the parcel deck roof)
2) which enables ripping out the existing P16 track and adjacent ultra wide P16 (with ramp from the parcel deck above) to give HS2 a wider work site.
I'm not sure if any HS2 siding would have been retained.
It is worth noting that the previous HS2 station design involved digging out to the equivalent of 4 floors below the current level and is unlikely to change in the new design.
There aren't many HS2 Euston area drone videos:
This is the most recent I could find quickly:
(I sure there have been more recent ones but search isn't finding them)
One overall HS2 and other infrastructure programme issue is that HMT's total annual capex limit is being hit across all sectors not just transport hence prioritising of some part of HS2 build (even with the core OOC - Birmingham station approaches) so the build will be longer overall.
So while it would make sense to be getting on with Delta Jn - northwards or OOC site prep (given the volumes to be removed from digging out) this will wait till a significant number of other structures north of the Chiltern Tunnel complete (the other useful effect is that requirement for civils staff and non specialised equipment is smoothed out).
Not digging out at Euston is actually probably quite useful in the short term will they start getting on with the Hampstead Road utility diversions (there will also be some buried tram track removal fun)