Article 79
[Amendment of the Basic Law]
(1) [...]
(2) [...]
(3) Amendments to this Basic Law affecting the division of the Federation into States (Länder), their participation in principle in tqhe legislative process, or the principles laid down in Articles 1 and 20 shall be inadmissible.
https://www.gesetze-im-internet.de/englisch_gg/englisch_gg.html#p0412
Basically says that the division into states (federalism) and the first 20 articles of the constitution can't be repealed or changed. Article 1-20 are fundamental and civil rights like human dignity, freedom of speech and religion, each person is equal before the law etc.
Freedom article, though I always found it weird to include a provision that states certain paragraphs can't be amended at all. Interestingly there's some debate among scholars whether Article 79 itsself can be repealed since it's not included in itsself.
Article 1
and Article 20 can't be repaled, not Article 1
to Article 20.
Of course the military draft (Article 12a) could be repealed, for instance. The fact that it has just been "suspended" instead of outright repealed is a result of not having the necessary two-third majority for such an action (like due to the opposition from the CDU).
Back in 1996, the Consitutional Court had also ruled that the right to asylum laid down in Article 16/16a could in theory be repealed altgother since such a action wouldn't violate the sanctity of human dignity of Article 1.