Power Automate offers several different trigger options for this:
1) When an item is created or modified
2) When an item or file is modified
The first one will trigger will all new entries and all modified entries. The second one will only trigger if it has been created previously and then modified. So this depends on if there are situations where you want the workflow to run with newly created items or with only modified items.
There are two ways you can do this for a specific value (one is more coding heavy than the other).
1) You trigger the workflow from your Sharepoint list and then you use a condition. You would put the value into the condition and then the workflow would only perform the actions if they match the value. This is very easy to set up and I build lots of flows using this. The other benefit is that you can stack several actions and workflows associated with this SharePoint list into 1 flow so you can have multiple different conditions doing different actions depending on the values/inputs.
2) You can make it so that the workflow only triggers with a specific value (more coding heavy). If you click on the three dots on the right side of the trigger action (first action of the workflow). Click on Settings. At the bottom, you can see "trigger conditions". You can add a trigger condition so that it will only fire if the value is met. Note that it needs to be written in the html Power Automate format and you can't use dynamic content. I typically figure out the dynamic content from copying and pasting it into a word document and then you can copy this for your trigger condition. This is very sensitive, so you have to make sure it is written correctly or the workflow won't fire at all.
