I'm not squirning; you're just ignoring the truth nd pretending it has not been shown to you.
#2. There is no OT command to "observe every day".

So they did not have to observe the Passover (Nisan 14th, which was SEPARATE from the days of unleavened bread, though Henry calls the whole period "Passover"), the Feast of Trumpets, the Day of Atonement, and the Last Great Day? Are you sure you want to claim that? LEt's go back to Lev.23. There, God calls ALL of them "holy convocations", (v.2), and then reiterates individually that they are holy convocations:
Feast of Trumpets: v24; Day of Atonement: v27; Last Great Day: v36. And the Passover was established in Ex.12, where it also was a separate event of "the whole assembly".
Where does God say that these other four days were optional? Let alone, where does Paul say that in contrast to the three being mandatory?
So the three days had a pilgrimmage of males, and you equivocate the concept of "mandatory" as referring to the
pilgrimmage only, yet all of those days were "holy convocations", to be OBSERVED in ONE WAY or another by ALL.
You are really straining to prove your point.
#4. BOTH practices (and both Examples) are being defended in Romans 14.
#5 EVEN if you Inject God's own Seventh-day Sabbath INTO the Romans 14 text - that would mean that keeping the 10 commandments IS allowed such that the arguments made AGAINST Sabbath Keeping (saying that it places us under the law) are void. Because if such arguments were true - you could not "defend" such an outcome. You could not argue "For those who want to be back under the law - let them believe it - its ok - they do so for the Lord". That is extreme opposite of the Galations 5 position and you end up with an internally - self-conflicted - text.
Well I don't say that you can't keep the sabbath, or that you are going back under the Law if you do. Just don't judge others for not keeping it. THAT's what brings you back under the Law. But you have to fight tooth and nail to rewrite this chapter to say something that never existed, because your whole MO would fall if you admitted its plain meaning.