Prints collapse when they get to bridges & islands

Hi, I am new to 3D printing, I recently bought an Ender 5 plus for my first printer with a sonic pad, I installed the black PLA filament they sent with it, did a couple of very small solid prints & no problems. I then did the all in one test print, but reduced by 75%, with it being black it was hard to see, so I changed to an alloy coloured filament, it would only print up to the bridges then the print would start to collapse, before long it was trying to print in mid air. I have looked into a lot of YT videos & following their settings I have adjusted the extruded feed rate, leveled the bed, done & saved a bed mesh etc, I changed to the whit filament supplied by Creality & it printed poorly, would not stick together and had a fluffy texture, so I went back to the ally filament, it print well on the 3D bench until it got to the point of starting the deck & islands, then it c
Started collapsing $ printing in air again.
What am I doing wrong?

Sorry that last part was got all messed up & can’t find how to edit a post, it was meant to read as, on a 3D bench print it gets to the deck to fill it in with the islands & the print starts to collapse & not stick to the underlying layer, it then starts printing in air.