ソレが

that

→ 其れ
phrase Rare #37,454
that ソレ is a stylized way to write それ, meaning “that.” The particle が marks it as the subject and can add emphasis or contrast.
JA: ソレが私の探していた本です。
EN: That is the book I was looking for.

ソレが年上や目上の者に対する態度か!

Is that any way to treat someone older or your superior?!

もしもソレが今日来たら?

What if it comes today?

— 別れる決心 (2022)

お母さんが亡くなった日ソレが?

The day Mom died? That one?

— 別れる決心 (2022)

ソレが入れてくれた

They put it in for me.

— 別れる決心 (2022)

ソレが来たのは月曜の何時?

What time did that arrive on Monday?

— 別れる決心 (2022)