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“QR & Barcode scanner” is Free an Open Source, and supports what you want (if i understood you correctly) https://github.com/wewewe718/QrAndBarcodeScanner
Looks like it’s not been updated in a while, but it works just fine. Available on F-Droid and on Google Play
Some key points regarding Proxmox:
For reference, my oldest Proxmox server is a 2013 AMD dualcore 16GB DDR2 ram with VMs on LVMthin on a single SSD, with legacy VM doing mdraid of 3 HDDs using hardware passthrough. Performance is still OK, the overhead from Proxmox is negligible compared to strain from the actual workloads