How do I make this in Survival?

Build the banner at a loom, then put the banner and a shield together at a crafting table. The banner is used up and the shield keeps the design.

Can I take the design off again?

No. Once a shield carries a banner it keeps it. A cauldron washes dye off leather armor, not off a shield.

How many layers can a shield have?

The same as a banner: six through a loom, and up to sixteen through a command.

Why does the shield look squarer than the banner?

Because it is. The shield's face is shorter and wider than a banner's cloth, so the same design is squeezed into it. That is how the game draws it too.

Does a patterned shield protect any differently?

No. It is decoration only, and the shield blocks exactly as much as a plain one.

Will this command work on Bedrock?

No. Bedrock writes item data differently. The design itself is fine there, so build it at a loom and combine it with a shield.

Minecraft Shield Designer

A shield takes any banner design. Build it here, see it on the shield, and copy the command.

2 of 16 layers

Base color

Layers, bottom first

Per Fess
Saltire

Add a pattern

The shield command

/give @s shield[base_color=white,banner_patterns=[{pattern:half_horizontal,color:red},{pattern:cross,color:black}]]

The same design on a banner

/give @s white_banner[banner_patterns=[{pattern:half_horizontal,color:red},{pattern:cross,color:black}]]

How it works

Pick the base color. On a shield that color is part of the item, not part of the banner.
Add patterns and set their colors. The preview is the shield, not a banner.
Copy the shield command, or note the layers and build the banner at a loom first.
The second command gives the same design as a banner, if you want both.

Java Edition commands. In Survival the route is a loom, then a crafting table.

Questions

How do I make this in Survival?: Build the banner at a loom, then put the banner and a shield together at a crafting table. The banner is used up and the shield keeps the design.
Can I take the design off again?: No. Once a shield carries a banner it keeps it. A cauldron washes dye off leather armor, not off a shield.
How many layers can a shield have?: The same as a banner: six through a loom, and up to sixteen through a command.
Why does the shield look squarer than the banner?: Because it is. The shield's face is shorter and wider than a banner's cloth, so the same design is squeezed into it. That is how the game draws it too.
Does a patterned shield protect any differently?: No. It is decoration only, and the shield blocks exactly as much as a plain one.
Will this command work on Bedrock?: No. Bedrock writes item data differently. The design itself is fine there, so build it at a loom and combine it with a shield.