I’m gonna put a massive asterisk on this response because I am a beginner but from what I understand having just taught myself Strapi → Digital Ocean deployment…
If I were you I would try to export the data on the local database and then ssh it to your Digital Ocean console and import it from there. Data getting overwritten upon deployment is a natural limitation of Strapi. So making use of their data managment features is necessary.
Also, I know that exact YouTube tutorial you mentioned - I recently taught myself how to host my Strapi backend on Digital Ocean as well lol. I believe it is outdated. I followed this documentation to get mine to work: https://docs.strapi.io/dev-docs/deployment/digitalocean-app-platform.