Questions in Tractate BM Chapter Two

Hello Rabbi,
I am studying Tractate BM Chapter Two…

1) In the article, the rabbi analyzed the difference between the Jewish perception of the Torah regarding the Sabbath of loss, which stems from an essential connection between the husband and the object, and the simplistic, secular perception of today that is conventional… The rabbi links this to the fact that Halacha is a religious system that is based on metaphysical perceptions (intellectual and not moral, as the Maharal put it)…
I'm not well-versed in law, but a friend of mine said that fundamental legal concepts were prevalent in the ancient world (Rabbi Shagar discusses this in his book 'Walks of the World', regarding tort law – grama, tzurorot, etc.)…
So why explain that the Torah has an interest in such a concept? Many rishonim (in the Mo'n, in the Kozari) understood the legal part of the Torah as the arrangement of society, which is a preparation for the divine virtues. In light of this, we are certainly obligated to the laws of the Torah, but we are not interested in such substantive concepts… And in any case, regarding the regulations and the law of the kingdom, one can be much more flexible, while mainly calculating the correction of society…

2) There is a topic that has been written about a lot, but I can't find a satisfactory explanation…
On page 21a, the Rosh writes that since the Gemara remains in the same position regarding half a cubit in four cubits, this is a question of Shabbat loss and must be declared… and similarly in page 25a regarding the question of Kashira and Kashura…

The Gra explains that he refers to doubt as doubt from isura and not doubt from mona, therefore one must be stricter.
The question is that the law of returning a lost thing stems from the question of ownership, and apparently one must first discuss the law of property… As the Mishkan of the Gerash regarding the prohibition of theft, here too one must first discuss whose property it is, and if it belongs to one's friend, one must in any case save one's property…
I saw that they brought in the name of Rabbi Feinstein (I did not find it) that only with regard to despair, the Rosh HaMir was stricter, in the absence of the law he would not be stricter because it is a question of judgment… But despair is also a question of judgment and not of the mitzvot of Shabbat Avidah, if the despair is not his and in any case he is not obliged to declare…