Matt 4:10 says (BLB):
Then Jesus says to him, "Get you away, Satan! For it has been written:
'You shall worship the Lord your God, and Him alone [μόνος] shall you serve.'"
This appears to quote Deut 6:13 -
[Hebrew] You shall fear only the LORD your God; and you shall worship
Him and swear by His name. (NASB)
The LXX text varies at this point, for example we have:
[Swete] Κύριον τὸν θεόν σου φοβηθήσῃ καὶ αὐτῷ λατρεύσεις, καὶ πρὸς
αὐτὸν κολληθήσῃ, καὶ τῷ ὀνόματι αὐτοῦ ὀμῇ. = Fear the Lord your God
and serve Him; and you shall cleave to Him, and in His name shall you
swear.
[Ellopos] Κύριον τὸν Θεόν σου φοβηθήσῃ καὶ αὐτῷ μόνῳ λατρεύσεις καὶ
πρὸς αὐτὸν κολληθήσῃ καὶ ἐπὶ τῷ ὀνόματι αὐτοῦ ὀμῇ. = You shall fear
the Lord your God, and him only shall you serve; and you shall cleave
to Him, and by His name thou shall swear.
It appears that Jesus, in Matt 4:10, quoted the latter form of the LXX. [The LXX is far from uniform!]
I also note that the word "only" [μόνος] is absent from Deut 10:20 in the LXX.