しか can mean 'nothing but' for example, in episode 3 of Over | Learn Japanese

しか can mean "nothing but"

for example, in episode 3 of Overlord Season 3, minute 13:45, the clerk says

アダマンタイト級冒険者でしかお引き受けできない案件でしょう

アダマンタイト級冒険者 = "adamantite-plated adventurer(s)
で = indicates a means here
しか = only with [the previously mentioned]
お引き受け = "undertaking" in this case, it's the request done to the adventurer(s)
できない = negative form of "can" or "able to" (so "cannot" or "not able to")
案件 = "matter" or "case"
でしょう = kind of like ですね, that is, like saying "right?" at the end of a sentence, but this is more formal, and could be taken as "I believe"

so the sentence is more or less

"I believe for this matter nothing but adamantite-plated adventurers are able"

if taken literally, a more natural translation would be

"I believe only adamantite-plated adventurers are able to undertake this matter", or "I believe only adamantite-plated adventurers can take this request" (taking into consideration the context of an adventurer's guild receiving requests)