As the reply above, the solution is to convert the string into a variable call, so that the change to /etc/default/connman can be properly processed.
Please, someone with powers, add the fix to debian/patches/01-init-script-lsb-headers.patch <https://salsa.debian.org/debian/connman/-/blob/debian/sid/debian/patches/01-init-script-lsb-headers.patch>. I would also like to request to anyone with powers to package thee fix when you have time after the bullseye release if not sooner. These would be the changes to said file, in case the petition is not understood: https://gitlab.com/nXecure/connman/-/commit/d5d43713977a5317c84b620251f3cdf2848598f2#8ec1dbece58825f4fe44c11e357d1993f9e23d81 Thanks for your time.
