I believe that there is no grammar point for 「しかし」
If I understand it well it’s a more common and shorter version of 「しかしながら」(https://bunpro.jp/grammar_points/674) but this one is in the JLPT1 course while 「しかし」 is listed as JLPT5 on https://jlptsensei.com/learn-japanese-grammar/しかし-shikashi-meaning/
JLPT1 is a long run away from the JLPT5, so maybe it would be a good idea to add it as another point in JLPT5.
References I could find on this grammar point:
- https://jlptsensei.com/learn-japanese-grammar/しかし-shikashi-meaning/
- 【だが】と【しかし】と【でも】の意味の違いと使い方の例文 | 例文買取センター
- https://hinative.com/ja/questions/6606758
- BUT in Japanese - でも vs けど vs が vs のに vs しかし┃the Native Way - YouTube [Japanese Ammo with Misa]
Edit: Now that I think about it, there is no grammar point for でも either, as in, used at the beginning of the sentence to mean “but”. Is it because it’s considered as a vocabulary point instead of a grammar one ?