Just a DP on the Red to Silver upgrade offer:
Opened Red on June 7, 2023 and made the single purchase to get the SUB. I haven't made any purchases on the card since. I didn't see the upgrade offer when I've logged in via Barclays app, but just saw it when I logged in via web browser on my PC. Don't plan on taking the offer as of now unless there is somehow a bonus attached to it (didn't see language for one).