Long story short, Linux uses n for a new-line, Windows rn and old Macs r. So there are multiple ways to write a newline. Your second tool (RegExr) does for example match on the single r. [rn]+ as Ilya suggested will work, but will also match multiple consecutive new-lines. (rn|r|n) is more correct.
eegex – match linebreaks – n or rn? – stack overflow, degex – match linebreaks – n or rn? – stack overflow, fegex – match linebreaks – n or rn? – stack overflow, tegex – match linebreaks – n or rn? – stack overflow, 5egex – match linebreaks – n or rn? – stack overflow, 4egex – match linebreaks – n or rn? – stack overflow, rwgex – match linebreaks – n or rn? – stack overflow, rsgex – match linebreaks – n or rn? – stack overflow, rdgex – match linebreaks – n or rn? – stack overflow, rrgex – match linebreaks – n or rn? – stack overflow, r4gex – match linebreaks – n or rn? – stack overflow, r3gex – match linebreaks – n or rn? – stack overflow, refex – match linebreaks – n or rn? – stack overflow, revex – match linebreaks – n or rn? – stack overflow, rebex – match linebreaks – n or rn? – stack overflow, rehex – match linebreaks – n or rn? – stack overflow, reyex – match linebreaks – n or rn? – stack overflow, retex – match linebreaks – n or rn? – stack overflow, regwx – match linebreaks – n or rn? – stack overflow, regsx – match linebreaks – n or rn? – stack overflow, regdx – match linebreaks – n or rn? – stack overflow, regrx – match linebreaks – n or rn? – stack overflow, reg4x – match linebreaks – n or rn? – stack overflow, reg3x – match linebreaks – n or rn? – stack overflow, regez – match linebreaks – n or rn? – stack overflow, regec – match linebreaks – n or rn? – stack overflow, reged – match linebreaks – n or rn? – stack overflow, reges – match linebreaks – n or rn? – stack overflow, regex ᰫ match linebreaks – n or rn? – stack overflow, regex &#u211; match linebreaks – n or rn? – stack overflow, regex &#i211; match linebreaks – n or rn? – stack overflow, regex ⏻ match linebreaks – n or rn? – stack overflow, regex ᾯ match linebreaks – n or rn? – stack overflow, regex q11; match linebreaks – n or rn? – stack overflow, regex w11; match linebreaks – n or rn? – stack overflow, regex ⁷ match linebreaks – n or rn? – stack overflow, regex ” match linebreaks – n or rn? – stack overflow, regex Rq1; match linebreaks – n or rn? – stack overflow, regex — match linebreaks – n or rn? – stack overflow, regex ̵q; match linebreaks – n or rn? – stack overflow, regex – natch linebreaks – n or rn? – stack overflow, regex – katch linebreaks – n or rn? – stack overflow, regex – jatch linebreaks – n or rn? – stack overflow, regex – mztch linebreaks – n or rn? – stack overflow, regex – mstch linebreaks – n or rn? – stack overflow, regex – mwtch linebreaks – n or rn? – stack overflow, regex – mqtch linebreaks – n or rn? – stack overflow, regex – march linebreaks – n or rn? – stack overflow, regex – mafch linebreaks – n or rn? – stack overflow, regex – magch linebreaks – n or rn? – stack overflow, regex – maych linebreaks – n or rn? – stack overflow, regex – ma6ch linebreaks – n or rn? – stack overflow, regex – ma5ch linebreaks – n or rn? – stack overflow, regex – matxh linebreaks – n or rn? – stack overflow, regex – matvh linebreaks – n or rn? – stack overflow, regex – matfh linebreaks – n or rn? – stack overflow, regex – matdh linebreaks – n or rn? – stack overflow, regex – matcg linebreaks – n or rn? – stack overflow, regex – matcb linebreaks – n or rn? – stack overflow, regex – matcn linebreaks – n or rn? – stack overflow, regex – matcj linebreaks – n or rn? – stack overflow, regex – matcu linebreaks – n or rn? – stack overflow, regex – matcy linebreaks – n or rn? – stack overflow, regex – match kinebreaks – n or rn? – stack overflow, regex – match pinebreaks – n or rn? – stack overflow, regex – match oinebreaks – n or rn? – stack overflow, regex – match lunebreaks – n or rn? – stack overflow, regex – match ljnebreaks – n or rn? – stack overflow, regex – match lknebreaks – n or rn? – stack overflow, regex – match lonebreaks – n or rn? – stack overflow, regex – match l9nebreaks – n or rn? – stack overflow, regex – match l8nebreaks – n or rn? – stack overflow, regex – match libebreaks – n or rn? – stack overflow, regex – match limebreaks – n or rn? – stack overflow, regex – match lijebreaks – n or rn? – stack overflow, regex – match lihebreaks – n or rn? – stack overflow, regex – match linwbreaks – n or rn? – stack overflow, regex – match linsbreaks – n or rn? – stack overflow, regex – match lindbreaks – n or rn? – stack overflow, regex – match linrbreaks – n or rn? – stack overflow, regex – match lin4breaks – n or rn? – stack overflow, regex – match lin3breaks – n or rn? – stack overflow, regex – match linevreaks – n or rn? – stack overflow, regex – match linenreaks – n or rn? – stack overflow, regex – match linehreaks – n or rn? – stack overflow, regex – match linegreaks – n or rn? – stack overflow, regex – match linebeeaks – n or rn? – stack overflow, regex – match linebdeaks – n or rn? – stack overflow, regex – match linebfeaks – n or rn? – stack overflow, regex – match linebteaks – n or rn? – stack overflow, regex – match lineb5eaks – n or rn? – stack overflow, regex – match lineb4eaks – n or rn? – stack overflow, regex – match linebrwaks – n or rn? – stack overflow, regex – match linebrsaks – n or rn? – stack overflow, regex – match linebrdaks – n or rn? – stack overflow, regex – match linebrraks – n or rn? – stack overflow, regex – match linebr4aks – n or rn? – stack overflow, regex – match linebr3aks – n or rn? – stack overflow, regex – match linebrezks – n or rn? – stack overflow, regex – match linebresks – n or rn? – stack overflow, regex – match linebrewks – n or rn? – stack overflow, regex – match linebreqks – n or rn? – stack overflow, regex – match linebreajs – n or rn? – stack overflow, regex – match linebreams – n or rn? – stack overflow, regex – match linebreals – n or rn? – stack overflow, regex – match linebreaos – n or rn? – stack overflow, regex – match linebreais – n or rn? – stack overflow, regex – match linebreaka – n or rn? – stack overflow, regex – match linebreakz – n or rn? – stack overflow, regex – match linebreakx – n or rn? – stack overflow, regex – match linebreakd – n or rn? – stack overflow, regex – match linebreake – n or rn? – stack overflow, regex – match linebreakw – n or rn? – stack overflow, regex – match linebreaks ᰫ n or rn? – stack overflow, regex – match linebreaks &#u211; n or rn? – stack overflow, regex – match linebreaks &#i211; n or rn? – stack overflow, regex – match linebreaks ⏻ n or rn? – stack overflow, regex – match linebreaks ᾯ n or rn? – stack overflow, regex – match linebreaks q11; n or rn? – stack overflow, regex – match linebreaks w11; n or rn? – stack overflow