In 1.15.2: If you had an item with a translation tag, like so:

/give @p minecraft:stone{display:{Name:'

{"translate":"item.custom.example"}

'}}

...and in your resource pack's language .json file, you had it written like so,

"item.custom.example": "§rTest Item"

Then in game, the item name would show up white, and unitalicized.

In 1.16.1, the same input & json files result in the name being shown as italicized. §r No longer seems to reset italics, for some reason, in json text files, and is instead treated like "color":"reset". The same is true of \u00A7r.

This is not true of bold, however. If, for instance, you were to use §l, the item shows up as bold. If you use §l§r, the item unbolds.

It is still possible to use, for instance,
/give @p minecraft:stone{display:{Name:'

{"text:"Test Item","italic":false,"color":"white"}

'}}
but this is suboptimal at best.

Essentially: as of 1.16, it is no longer possible to unitalicize custom item names within language .json files. All other formatting works fine. The §r reset formatting just does not work fully in 1.16.1.