There actually are three versions involved. Your source (Heroku) is 13.9. Your app is 11.18. And the DB is running 14.4.
Try reapplying this change: Error failed to fetch an image or build from source...Unknown desc = quay.io/evl.ms/fullstaq-ruby:3.0.1-jemalloc-bullseye-slim: not found - #11 by SimBed :
ARG RUBY_VERSION=3.0.1
ARG VARIANT=jemalloc-buster-slim