What causes these strange objects to flash up on boot screen?

@livfe - My answer was generic across any Mac system which uses main RAM as a video buffer when using the supported macOS.

Try cleaning the RAM chips pins using a stiff toothbrush and 90% isopropyl alcohol, then apply some flux and reheat the solder joints touching up with some solder using a hot air re-work system

@danj Yes, but this is regarding a 2014 MacBook Air....Is there a 'fix' for this?

@livfe - Cleaning and re-soldering the RAM chips or replacement if you can identify a bad chip. The tantalum capacitors within the RAM support logic could be bad or just tired.

@Dan ???? You want this person to literally do something that would cost more time and money for something that he is selling? And making a grand assumption without even seeing any of the capacitors on the board? Screen flickering is very broad and happens on a lot on older systems during boot, it could very well be a bad capacitor but if it’s not happening after it boots up it could really be anything from a cap to power supply, to drivers. I wouldn’t expect someone to really care that much or even notice it for a 75$ laptop at best. I’m just making an assumption but if this person is selling I doubt they have the flux or even tools to test every single capacitor and disassemble the whole thing to test every single cap or even worse introduce new problems like completely frying the screen but the cap was put on the wrong. It’s common with MacBooks, possibly a capacitor, will continue to work until it doesn’t and even then you could just hook it up to a secondary monitor.

And to suggest to re soldering the ram chips which is beyond beginner level which they wouldn’t be here asking for help if they had equipment or time