[ETP Not Found Error]

You're not using it correctly.   You need to enter in your two ETOPS diversion airports that represent the ETOPS leg or operation area of that route.  So if (for example) were flying from JFK to HNL, you'd properly plan for SFO as your diversion airport once you enter the ETOPS segment (60 minutes beyond a nearest suitable landing site).  OGG or maybe HNL would be your closest diversion point on the other side.  So you are required to calculate, plot, and monitor your ETP between those two diversion airports.  For that example, you'd enter KSFO and PHOG into the Equal Time Point page.  Remember, to refer to your ETOPS section in the OFP.  It has already assigned your ETOPS diversion airports for you, and calculate the ETP between those airports.   

[Cabin curtains]

Is there any chance the cabin curtains could be left open by default instead of closed?  This would be a more realistic configuration when first entering the aircraft and during boarding.

[LOC and G/S not activated]

I've had the same issue twice now.  Last night flying into KDEN ILS 35R, and again tonight heading back into EGLL ILS 09L.  LOC and GS never capture,  and remain blue. 

[Why can't the a350 do 19 hours from KJFK TO WSSS]

Ultra long haul flights are very weight restricted.  Try bumping that 16,000 pounds of cargo, and reducing your passenger load a little.   See if that helps. 

[350 Not loading Navigraph charts in FS2020 and 2024]

Seeing the as here as well. MSFS2020.

[Is this normal?]

I have the same issue with no way to disable the default OMDB scenery.