Minecraft Windows 10 edition testfor command

Even though there's no NBT, there are data values for different types of potions.

You can use clear in a repeating command block to clear all the potions of a particular type and use a comparator to unlock the door.

Put this in a repeating command block:

clear @a potion <data value>

where the <data value> is one of the following (from the wiki):

┌─────────────────────────────┬─────────┬──────────┬──────────┐
│           Potion            │ Regular │ Extended │ Enhanced │
├─────────────────────────────┼─────────┼──────────┼──────────┤
│ Water Bottle                │       0 │          │          │
│ Mundane Potion              │       1 │        2 │          │
│ Thick Potion                │       3 │          │          │
│ Awkward Potion              │       4 │          │          │
│ Potion of Night Vision      │       5 │        6 │          │
│ Potion of Invisibility      │       7 │        8 │          │
│ Potion of Leaping           │       9 │       10 │       11 │
│ Potion of Fire Resistance   │      12 │       13 │          │
│ Potion of Swiftness         │      14 │       15 │       16 │
│ Potion of Slowness          │      17 │       18 │          │
│ Potion of Water Breathing   │      19 │       20 │          │
│ Potion of Healing           │      21 │          │       22 │
│ Potion of Harming           │      23 │          │       24 │
│ Potion of Poison            │      25 │       26 │       27 │
│ Potion of Regeneration      │      28 │       29 │       30 │
│ Potion of Strength          │      31 │       32 │       33 │
│ Potion of Weakness          │      34 │       35 │          │
│ Potion of Decay             │      36 │          │          │
│ Potion of the Turtle Master │      37 │       38 │       39 │
│ Potion of Slow Falling      │      40 │       41 │          │
└─────────────────────────────┴─────────┴──────────┴──────────┘

^{sorry mobile users}

Then put a redstone comparator next to it, which will output a signal strength equal to the number of items removed.

You can use /clear<player> netherite_sword -1 0. The -1 matches all data values* and the 0 specifies the maximum number of items to clear (so none will be cleared). If the player has at least 1 netherite sword in their inventory, the command will output a success.

The success can be detected using a chain command block. Put the /clear any command block facing a conditional, always active, chain command block with the command that you want to execute if the player has a netherite sword.

^{* I'm not sure if a sword has any data values (e.g. for durability) so just match all data values instead of 0 just in case.}