I generally will not upgrade sql instances and will create a new instance and restore a backup to that. With that being said there is no way to restore a database from a newer version of sql to even one version behind it. If you are dead set on doing that you can script out the database and then run the scripts to recreate it but that is not something I would even consider doing.
I've run RMS with sql 2019 and before that 2017 and so on with no issues. Are you patched to 2.0.2023? If not I would start there and then I would work on optimizing sql and troubleshooting from there. Is SQL running on its own dedicated server/ computer? Does the operating system have at least 8GB of RAM? The sql buffer cache in sql express can only use 1GB, but I usually set the max memory to 2-4GB depending on the system. How large is your database and how many clients are accessing it? You may want to try setting up a new sql developer instance and if that performs better then go ahead and purchase a sql standard server/ cal or core license. Do not use sql dev in production or that can cost you greatly in an audit.
