There are several GUIs for Neovim because it externalises the user interface elements, so any GUI can draw these in different ways. There's a list that tracks the status of these projects. My favourites are FVim and goneovim and both support remote sessions
I believe gvim --remote is what you're looking for.
If no GVim is running, it will start a new instance of it, but if an instance is already running, gvim --remote will open the file on that instance and raise its window.
See :help --remote for details. You might also like --remote-tab to open the file in a new tab.
If you set your file associations to ...
This is a normal behaviour of gui flavours of vim like gvim. <m-i>, <a-i> and é are the same thing.
Usually people aren't bothered by meta+key inserting an accentuated character, but the other way around. See the very old issue with French people needing to insert é in LaTeX document which in turn triggers \item insertion (IIRC) with vim-latex.
I find a way myself -- a python module rpdb - remote debugger based on pdb.
It works for me.
Install using pip install rpdb
Set breakpoint with rpdb.set_trace() in plugin python script.
Try to active the plugin in vim. The vim will hang-up.
Use telnet to connect the vim process. telnet localhost 4444. It will be same as pdb to use.
A solution to this problem is mentioned in Vim's documentation (:h --remote). The following command should open filename to line_number:
gvim --servername DEBUG --remote-send "<C-\><C-N>:tab drop filename<CR>line_numberG"
Note that this seems to neither raise nor focus Vim. And I believe that opening the file using :tab drop ...