Nr. 4 is in the passive voice.
"I was delighted with…" - I'd say this is just a simple adjective as in: "I was happy…"
"I was stressed/frightened/confused" - it depends on what follows.
"I was very stressed etc." = "I was very nervous etc." - adjective
"I was frightened by my brother." meaning "My brother frightened me." - passive
Generally people agree that if we (can) use "by", it is in the passive voice, if we don't/can't or there's another preposition, it's an adjective.
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