QR codes essentially just encode text, as long as you're using a sensible QR code reader and check any URLs before opening them there's minimal risk to scanning a QR code.
I may have in the past put lyrics from “Never Gonna You Up” or links to the music video on YouTube in QR codes I printed on blank business cards and left them in public places around town.
Okay, but who’s is doing guerrilla advertising for a centralized service that requires a SIM card & an Android/iOS primary device or no account for thee. …At least in the past I convinced grandma this is the new SMS app you can use as I knew she would treat it as such, but now I wish I hadn’t since even that useful feature was lost. I want to drop Android entirely, but I need access to my contacts locked in the Signal system--which centralized system lock-in is one of the things we privacy-concerned folks want to avoid.