If you want to set your modpack version statically to avoid any modpack updates that could interfere with your gameplay, you can use these steps to easily set the version to avoid this. This is an advanced guide, so remember to use at your own risk.
1. Install your modpack using this guide.
2. Open the File Manager
3. Right click docker-compose.yml
and click Edit
4. Add a new line under TYPE: AUTO_CURSEFORGE
that says CF_FILENAME_MATCHER
5. In my case, I'm using Better MC 4, so I can choose a version such as v16 and set it to that version. Depending on the modpack, the version number may be something similar to 8.1.1 or 7.1.1, so you can set this to that number.
6. Save the file and Save the Basic Server Settings