It sounds to me like you are inserting the driver tip directly into the drill. You will need to use the silver 1/4” driver in the drill first. It has a notch at the end designed to lock into the impact. Then the tip goes into the driver and that should be held in with either a magnet or a wire ring inside the silver driver.
Just buy a new saw. It’s not much more than what a new motor would likely cost you.
https://www.toolsid.com/dewalt/14-abrasive-chop-saw-electric-mpn-d28710.html?view=042084&utm_source=microsoft&utm_medium=cpc&utm_campaign=268680567&utm_content=1173179535357969
I just Went into a service center to have my 40v blower repaired and they’re are switching around some model numbers and changing some things. They had a hard time ordering a replacement due to this.
https://www.dewalt.com/products/power-tools/shop-by-cordless-platform/40v
Lots of sites have it in stock. Looks like the option with batteries is discontinued though. https://www.dewalt.com/products/gear-and-equipment/generators-and-portable-power/1800-watt-portable-power-station-and-simultaneous-battery-charger/dcb1800b
I’ll give you that it’s a hair too short but I rip 8’ sheets regularly. There’s a finite amount of wiggle room to set the track on a 8’ rip for it to work properly. Takes a few minutes to figure out but once you do, mark your track so it’s easily setup next time.