ok, try this:
- Copy the code below to your clipboard.
- Add a new action in your flow after your "HTML to text" action"
- Click on my clipboard.
- Click paste.
A bit like this:

Except your one is called getURL. Because a couple of the concepts are a little complicated I have separated the actions into different steps, so you can better understand what is going on.
After you paste, you will have a scope which will contain the steps that give you the URL, but these are intended to be chained off the action, HTML to text, so must go after it.
{"id":"2b75eb54-de4b-4cb5-8ab0-96c4-e6bf1982","brandColor":"#8C3900","connectionReferences":{"shared_conversionservice":{"connection":{"id":"/providers/Microsoft.PowerApps/apis/shared_conversionservice/connections/shared-conversionser-8c945934-2489-4e84-98ab-725c-31760fc1"}}},"connectorDisplayName":"Control","icon":"data:image/svg+xml;base64,PHN2ZyB3aWR0aD0iMzIiIGhlaWdodD0iMzIiIHZlcnNpb249IjEuMSIgdmlld0JveD0iMCAwIDMyIDMyIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPg0KIDxwYXRoIGQ9Im0wIDBoMzJ2MzJoLTMyeiIgZmlsbD0iIzhDMzkwMCIvPg0KIDxwYXRoIGQ9Im04IDEwaDE2djEyaC0xNnptMTUgMTF2LTEwaC0xNHYxMHptLTItOHY2aC0xMHYtNnptLTEgNXYtNGgtOHY0eiIgZmlsbD0iI2ZmZiIvPg0KPC9zdmc+DQo=","isTrigger":false,"operationName":"getURL","operationDefinition":{"type":"Scope","actions":{"startPos":{"type":"Compose","inputs":"@indexOf(outputs('Html_to_text')?['body'], 'https://docs.google.com')","runAfter":{}},"endPos":{"type":"Compose","inputs":"@indexof(substring(outputs('Html_to_text')?['body'], outputs('startPos')), 'sharing')","runAfter":{"startPos":["Succeeded"]}},"URL":{"type":"Compose","inputs":"@substring(outputs('Html_to_text')?['body'], outputs('startPos'), add(outputs('endPos'),7))","runAfter":{"endPos":["Succeeded"]}}},"runAfter":{"Html_to_text":["Succeeded"]}}}
See how you get on.