Obsidian Farms
Obsidian Farms are significantly modified on Vanilla+ due to Wither behaviour being changed on Vanilla+ to improve server performance.
Due to these changes, the majority of YouTube or TMC Catalogue 1.21 overworld obsidian farms do not work on Vanilla+.
End Obsidian Farms
There are a plethora of end obsidian farm designs floating around, however this design by Dropjawed is designed with Vanilla+ mechanics in mind and is extremely compact, while avoiding any pointless extra steps.
Overworld Obsidian Farms
If you have any knowledge of a 1.21 overworld obsidian farm that works on Vanilla+ and has been tested for multiple hours, please DM "dropjawed" on Discord.