Markdown in Spyder IDE

No. As far as I know Spyder IDE has no markdown implemented as Jypter notebook even if it is connecting to a Jupyer notebook instance locally.

I would suggest you to use Jupyter notebook for coding and annotation if you need such a thing. Spyder is just a IDE. But if you want to edit Jupyter notebook in a IDE just take a look at PyCharm IDE.

If you want to comment/uncomment you could use CTRL +1 to change a single line, and with CTRL+4 you could change an entire block.