actions have disappeared

Do you have action set somewhere on your hard drive? Is that your set or downloaded from the internet? Perhaps you still have it somewhere on hard drive. Downloaded actions are not necessary in default folders, you can keep them anywhere you want. Same thing with actions recorded by you, you could save them anywhere.

When you load actions downloaded from internet in Photoshop, that is duplicate or copy of actions. Original file is still in its place unless you delete it.

It is like with images, when you open image you can work with it but original is still on hard drive. If you do not regularly save image you may lost it. Same thing with actions, if you open and change/modify or record your own actions you must save them otherwise you are in risk to lose them.

More here:

https://prepression.blogspot.com/2017/01/photoshop-custom-action-file-backup.html

https://raw.githubusercontent.com/MarshySwamp/Backup-Photoshop-Settings/main/Open%20Photoshop%20Presets%20%26%20Settings%20Folders

You may have a copy of the .psp file from an earlier install if you have not saved out to .atn file.

Did you migrate your Photoshop presets. Try menu Edit>Presets>Migrate Presets. Always save your actions sets into *.atn file so you can load them should your Preferences get reset.  You should always save Actions you add and edit  for safe keeping. Save them into to you own folder not one Adobe creates.,