Hello Paulo,

i was just digging the same right now and after some try and fail and inspiration in OCA it's looks like the whole magic in in the way how you add submodule. 

git submodule add -b main repo path && git commit -a && git push -u origin Develop

replace path with something like this company/monorepo

in .gitmodules you can see the difference 

[submodule "l10n_cz_bank_systee"]

​path = l10n_cz_bank_systee

​url = git

[submodule "systee/l10n_cz"]

​path = systee/l10n_cz

​url = git

​branch = main

From this moment you will see in your odoo.sh log new adoon_path (but for repo that is without / in path it will be added to /home/odoo/src/user)

odoo: addons paths: ['/home/odoo/src/odoo/odoo/addons', '/home/odoo/data/addons/17.0', '/home/odoo/src/user', '/home/odoo/src/user/systee/l10n_cz'] 

So this is the magice :) 

it's also mention in doc but without information about / in path what's happen