Q: Who are the "chiefest apostles" in 2 Cor.11:5?
The supper-apostles in (v5), Paul identifies in v-4 as those who proclaim - “another Jesus; .a different Spirit; a different gospel,” not the gospel preached by “Apostles - the twelves.”
They were itinerant, self-appointed Hebraic Jewish believers, i.e. (Acts 15:1-21; Gal. 2:1-5). Paul was firm against them and even without hesitant pronounced, repeatedly, a curse on those itinerant "supper apostles" who spread "another Gospel(Gal 1:6-9).
Those so-called "Supper-apostles" were propagating, as Paul termed,
"Another gospel" = the Word + their traditional teachings.
And such a false gospel confused the Antioch church (Acts 15).
It is worth to note, one of the hallmarks of the "super-apostles" is the "tare- spirit"(Matt. 13:24-30) working in them. They were in effect "making void the word of God with their traditions (Mk. 7:13), and thus "breaking the Scriptures" (Jn. 10:35).
The same tare - spirit is still at work among Christendom confusing the Word and has caused discord and divisions in the Body of Christ.
Apostle John says, do not believe every spirit but test (1 John 4:1), and that responsibility falls on each matured Believer (https://www.biblestudytools.com/hebrews/5-14.html).
Jesus sent the Holy Spirit -"another Helper (ἄλλον Παράκλητον), and said when the Holy Spirit-the Spirit of truth comes, He will guide into all the truth and do more (Jn. 14:17, 26; 16:13). When we yield ourselves to the Holy Spirit and the Word, we will not be deceived.
The "super-apostles" will not be there for us, but we will stand at the door!