There is is you use Optifine, which the OP clearly appears to be using due to the "OF" logo (I can't confirm whether they show the Optifine editor since I don't have 1.13.2+, which is apparently required to change the cape in-game, either way, i do not know of any other current mods that let you have your own capes (which are technically not allowed by Mojang, even for free, not sure how Optifine gets away with "selling" capes).
All that comes up is this
There are no custom capes on Java edition.
There is is you use Optifine, which the OP clearly appears to be using due to the "OF" logo (I can't confirm whether they show the Optifine editor since I don't have 1.13.2+, which is apparently required to change the cape in-game, either way, i do not know of any other current mods that let you have your own capes (which are technically not allowed by Mojang, even for free, not sure how Optifine gets away with "selling" capes).
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?