There are two questions here:
how to cite?
can (and how) such materials be used?
The first question can be certainly answered. Library Guides from Victoria University has the following example in APA style:
Ooi, D. (2018). AEB1804: Young People in a Global Community, week 1, session 1 notes [Course Presentation]. Retrieved from https://vucollaborate.vu....
First of all, this doesn't look like a reviewer's comment, but rather like a copy-editor's comment. And if I interpret the comment correctly, they just want a note that indicates when the resource was last accessed for all online resources. So you only have to add "(Accessed 10 January 2020)" after the URL.
This is completely unrelated to the age of the ...
If they're objecting to your citation style, don't worry. They are hardly going to recommend rejection because your citation style is wrong (or even if they do the editor is unlikely to actually reject for that reason). The journal's production staff will fix it for you if/after your paper is accepted.
For figures, one can include a figure credit in the caption, something as simple as “Figure credit: Zerothehero, unpublished lecture notes.”
The same holds for theorems:
Theorem: [Zerothehero, unpublished lecture notes] The Sun rises in the East.
Theorem: The Sun rises in the East [see also Zerothehero, unpublished lecture notes]
You might also ...
Open source software is used everywhere. For all example, nearly all of High Performance Computing, and the entire field of Computational Science and Engineering (CS&E) works with open source software, and does so very successfully. Furthermore, these packages are often at least as good or better than what commercial packages can offer. Many of these ...
Yes, open-source code can be used for research if it is cited everywhere you use results from it. You may first like to verify that the code is indeed open-source by verifying that the license is one of these: https://opensource.org/licenses
This should be listed clearly on the website/repository/license/readme file. If this is not available, try contacting ...
What do your readers need to know to appreciate the main result of your paper? If your paper builds on the ideas of others, these ideas must be stated (included explicitly) and accompanied by a citation. If you simply note in passing that there are other relevant ideas, reference may be enough. Having said that, as a reviewer, I will question ...
There is no API for google scholar data. They do that on purpose ...
Here are links to some possible workarounds