Review that passage again from Exodus 31 once again:
Exodus 31
12 And the Lord spoke to Moses, saying, 13 Speak also to the children of Israel, saying: Surely My Sabbaths you shall keep, for it is a sign between Me and you throughout your generations, that you may know that I am the Lord who sanctifies you. 14 You shall keep the Sabbath, therefore, for it is holy to you. Everyone who profanes it shall surely be put to death; for whoever does any work on it, that person shall be cut off from among his people. 15 Work shall be done for six days, but the seventh is the Sabbath of rest, holy to the Lord. Whoever does any work on the Sabbath day, he shall surely be put to death. 16 Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations as a perpetual covenant. 17 It is a sign between Me and the children of Israel forever; for in six days the Lord made the heavens and the earth, and on the seventh day He rested and was refreshed.
You had highlighted v.13 above to draw attention to "
My Sabbaths". I repeated your highlight to make it easier for you to see.
It doesn't refer to God's "Sabbath".
It calls attention to God's
Sabbaths in the
plural.
That means all of the Sabbaths ordained by God in the Mosaic covenant, and not just the weekly cycle.
For some reason you seem to think that drawing attention to God's claim of ownership of the Sabbath He ordained scores you something in an argument. I have no idea what your point is.
Did you think anyone here believes Daffy Duck ordained the Sabbath?

No.
God did, the same God called on by the pronoun "
He" in Hebrews 10:9 that states "
He takes away the first that He may establish the second". The right of ownership God retains as Creator is the same right He exercises when He took away the first covenant - which includes the Sabbath by ending ordinances demanding burnt offerings God has no pleasure in (review the context).