Closely relates to MC-54988, and likely also MC-241321.
The bug
The redness effect which can be seen around the edges of the screen when near the world border will be hidden if the player presses F1.
Whether or not this is intended is unclear, as many other tickets in this vein have been either fixed or considered intentional; input from Mojang is needed on this matter. The following list is of tickets involving similar effects that disappear(ed) with F1 and their resolutions:
MC-73730: darkness vignette - awaiting triage/resolution
MC-196469: nausea green tint - was fixed
MC-83353: nether portal overlay - considered intentional
MC-121536: carved pumpkin overlay - considered intentional
MC-203575: spyglass overlay - considered intentional
MC-205029: powder snow overlay - considered intentional
How to reproduce
Get close to, or past, the world border
Press F1
Note that the red haze at the corners of the screen disappears
Expected results
Pressing F1 would have no bearing on this red vignette effect - it has extreme similarity to the nausea haze.
Actual results
F1 shows or hides this effect.
1.16.1 and older affects