UPDATE: Someone downvoted this question: I'm not trying to be disrespectful, I appreciate instead please giving me constructive feedback, if I should rephrase - but I've edited the original post, to make things clearer. Also: I suspect neovim/nvim isn't loading ~/.vim/coc-settings.json but I thought sourcing like shown would fix that and is it possible to see some kind of vim/neovim initialization log? So, the /home/user/.vim/coc-settings.json must be okay (since vim uses it). I also found out that I could "debug" a bit using the output from ":CocInfo" - this also reveals that the language server using nvim doesn't start at all... There are no errors/warnings, just nothing happens. - the difference should be very clear from the below?
=== 1: vim ===
## versions
vim version: VIM - Vi IMproved 8.2 8022380
node version: v15.7.0
coc.nvim version: 0.0.80-1e2652e725
coc.nvim directory: /home/user/.vim/plugged/coc.nvim
term: dumb
platform: linux
## Log of coc.nvim
2021-02-19T21:39:22.868 INFO (pid:1355597) [services] - registered service "languageserver.fortran"
2021-02-19T21:39:22.872 INFO (pid:1355597) [services] - fortran state change: stopped => starting
2021-02-19T21:39:22.907 INFO (pid:1355597) [plugin] - coc.nvim 0.0.80-1e2652e725 initialized with node: v15.7.0 after 100ms
2021-02-19T21:39:22.913 INFO (pid:1355597) [language-client-index] - Language server "languageserver.fortran" started with 1355608
2021-02-19T21:39:27.165 INFO (pid:1355597) [attach] - receive notification: showInfo []
=== 2: nvim ===
## versions
vim version: NVIM v0.4.4
node version: v15.7.0
coc.nvim version: 0.0.80-1e2652e725
coc.nvim directory: /home/user/.vim/plugged/coc.nvim
term: xterm-256color
platform: linux
## Log of coc.nvim
2021-02-19T21:39:59.762 INFO (pid:1355680) [plugin] - coc.nvim 0.0.80-1e2652e725 initialized with node: v15.7.0 after 113ms
2021-02-19T21:40:02.607 INFO (pid:1355680) [attach] - receive notification: showInfo []