Should I change the silence mode for text messages or leave it as is?

I would not move to an unstable Silence build just for SMS scams. The scam part is mostly the phone number/carrier side, so a different SMS app will not really solve that. If they only need normal SMS, I would pick a maintained simple app like QUIK SMS and deny optional permissions; keep Silence only if they still use its encrypted chats with someone. The older Android/LineageOS version is probably the bigger security concern than the SMS client itself.