if *all* lines in /etc/apt/sources.list.d/myrepo.sources are
indented by a few space chars, then these lines are silently
ignored. This is unexpected. deb822(5) mentions lines starting
with # are ignored, but leading space chars are only documented
for continuation lines in folded fields. If the very first line
is indented it is obviously not a continuation line.

I would suggest to show at least a warning, or (even better)
drop this weird format altogether in favour of standard yaml
or json files.

Regards
Harri