In Telescope by default you can use <C-v> to open the current element in a vertical split. The mapping seems to still be present in the telescope picker of nvim-devdocs, however it throws an error when used (same thing happens when using <C-x> and <C-t>):
E5108: Error executing lua: vim/shared.lua:0: s: expected string, got function
stack traceback:
[C]: in function 'error'
vim/shared.lua: in function 'validate'
vim/shared.lua: in function 'gsplit'
vim/shared.lua: in function 'split'
...kages/start/telescope.nvim/lua/telescope/actions/set.lua:162: in function 'run_replace_or_original'
...ckages/start/telescope.nvim/lua/telescope/actions/mt.lua:65: in function 'run_replace_or_original'
...ckages/start/telescope.nvim/lua/telescope/actions/mt.lua:65: in function 'run_replace_or_original'
...ckages/start/telescope.nvim/lua/telescope/actions/mt.lua:65: in function 'key_func'
...Packages/start/telescope.nvim/lua/telescope/mappings.lua:269: in function <...Packages/start/telescope.nvim/lua/telescope/mappings.lua:268>
I think this could be fixed by replacing the select_(vertical|horizontal|tab), actions as it is done in https://github.com/nvim-telescope/telescope.nvim?tab=readme-ov-file#default-mappings for select_default.