Should the Tyne & Wear Metro be listed in the signaling section on OpenRailwayMap as PZB since that is the closest to the signaling system it uses?

Waterloo and City: depot area is the whole semi-open area under Spur Road (ie, centroid more to South-West).

https://www.openstreetmap.org/node/3359292021 - is it located underground?

In such case location=underground would be nice.

Or maybe level tag if it this location has levels.

Note that layer=-1 doesn't mean it's underground.

Foot bridge reportedly demolished. https://www.reddit.com/r/london/comments/qo40nq/the_pedestrian_bridge_in_waterloo_got_demolished/

It is not called the Elizabeth Line West of Westbourne Park Turnback sidings, it is the GWML. There is more non Elizabeth Line services than Elizabeth Line services on the GWML. Even the GWML relief lines which is the main lines which the Elizabeth Line runs on still has mainly got non Elizabeth Line services. Also the lack of speed limits shown on the GWML Relief lines. https://sacuksprodnrdigital0001.blob.core.windows.net/sectional-appendix/Sectional%20Appendix%20full%20PDFs%20December%202022/Western%20Sectional%20Appendix%20December%202022.pdf

Tracks for Platform 11 & 12 are currently buffer stopped near this point. Is it to be permanent?

There are two new railway tracks here, to the North of the flyover

As far as I can tell, there's no etcs west of airport junction

https://webinfo.uk/webdocssl/irse-kbase/ref-viewer.aspx?RefNo=1620402651&NextPrevious=YES&_height=732&_width=412

https://www.railengineer.co.uk/crossrails-signalling-challenge/

Could the SWML be edited to show the landslip and the reduction to signle line working on the Up Slow and while they are in the process of sluing over the Down Fast on to the Up Fast.

Track is disused, not abandoned, the rails are still in place. The New North Mainline, rails still are there. the maps you referred to showing it being lifted show the track still there, also you can still see all of the track from a passing train. So it should be tagged as Disused and not Abandoned.