Wasn't this fixed at some point? I seem to recall it was almost gone for a while. It is quite bad now. Stations, electrification in particular seem to frequently clip with vehicles and flicker obnoxiously.
(https://i.imgur.com/619yPtw.png)
The graphics code has never been changed specifically for Extended, so any issue in Extended will be the same as in Standard. It may be that it has been fixed in Standard too recently to have been incorporated yet - I know that Andrew Carlotti was working on merging the latest changes from Standard, but this was taking him a long time.
If the engine needs all the time for simulation, it may switch to the old, but much faster redraw routines to catch up. If the idle time in the display option dialogue is consistently zero and the frames per second are below target, then this may be the case.