We had the same problem with nopCommerce450 running on Debian Bullseye with MySQL 8.0.
Suddenly the application wasn't available any more. We found out that the reason was the unattended update from MySQL 8.0.21 to 8.0.29. After that the nopCommerce service couldn't start anymore.
We solved this issue by replacing the existing MySql.Data.dll library with the actual one for release 8.0.29 by the following steps:
1. Download Connector/Net 8.0.29 from website https://dev.mysql.com/downloads/connector/net/.
Select .NET & Mono
2. Unzip the file in any directory
3. Go to subdirectory v4.8. There you will find the file MySql.Data.dll.
4. In this directory run the command : gacutil /i MySql.Data.dll as root or by sudo command
5. Replace the current file MySql.Data.dll by the new one from the unzipped download-file.
6. Restart service nopCommerce