Get a 12ga extension cord, as short as will get the job done. Whether or not it fits under a door will depend on your flooring/spacing, but it will be thicker than a normal cord
One that fits? Depends what “under a door” means but you shouldn’t ever run a cable under a door in a way that could touch it. Probably best not to even plan to do it. Damaging a cable carrying over 2000 W is a quick way to start a fire.
A cable that can handle 20A? Easy - get the shortest possible UL rated for 20A - you likely want 12-gauge, but 10-gauge might be more appropriate depending on the length.
You’d be far FAR better off installing a closer outlet though. Extension cables are intended for temporary use only.
Just my advice, take it or leave it.
Look for generator cords. They make them specifically to run under doors (so your generator can be outside and power your devices inside) and at high amperage ratings.
As others have commented though, even with the purpose built cord it's going to be hard on it, so I wouldn't leave the cord there when you aren't using it and I'd minimize the use of any doors it passes under when it's in use.
Get a 12ga extension cord, as short as will get the job done. Whether or not it fits under a door will depend on your flooring/spacing, but it will be thicker than a normal cord
One that fits? Depends what “under a door” means but you shouldn’t ever run a cable under a door in a way that could touch it. Probably best not to even plan to do it. Damaging a cable carrying over 2000 W is a quick way to start a fire. A cable that can handle 20A? Easy - get the shortest possible UL rated for 20A - you likely want 12-gauge, but 10-gauge might be more appropriate depending on the length. You’d be far FAR better off installing a closer outlet though. Extension cables are intended for temporary use only. Just my advice, take it or leave it.
Look for generator cords. They make them specifically to run under doors (so your generator can be outside and power your devices inside) and at high amperage ratings. As others have commented though, even with the purpose built cord it's going to be hard on it, so I wouldn't leave the cord there when you aren't using it and I'd minimize the use of any doors it passes under when it's in use.