This is a a very quick 'How to' on getting the Tenant ID.
This question does not require an answer, it's just here for reference.
An example of how you might use this is when providing a flow for someone to import, that requires the Tenant ID, and you are not giving them any work to do. I'm there are plenty of other use cases, my main one is ensuring it is the Tenancy ID without a bad copy/paste from somewhere else.
The Flow
Here's an image of what is needed:

The Actions
These actions will take you there.
HTTPS GET GetMyProperties
This call is made in whichever site you are currently a member of and wish to use on the target tenancy.
The Uri key value is as follows:
_api/SP.UserProfiles.PeopleManager/GetMyProperties
FilterToSPSDistinguishedName
This is where you will filter to the exact required property that you need. If you name your HTTP action differently I hope that it is obvious that you need to change the reference to that accordingly.
This is the From key value is as follows:
@body('HTTPS_GET_GetMyProperties')?['body']?['d/UserProfileProperties/results']
If you have named your HTTPS action identically you can paste that in.
This is the where value:
| Left |
Middle |
Right |
@{item()?['Key']}
|
is equal to |
SPS-DistinguishedName |
You should be able to paste in the left and right sides, and you may find some success pasting in the below spoiler as the full action.
Spoiler (Highlight to read)
{"id":"0956922a-0427-4948-9fd2-e65cf0dd8e0e","brandColor":"#8C6CFF","connectionReferences":{"shared_sharepointonline_1":{"connection":{"id":"/providers/Microsoft.PowerApps/apis/shared_sharepointonline/connections/shared-sharepointonl-70a14524-6d74-4196-b1fc-31d350117f82"}}},"connectorDisplayName":"Data Operations","icon":"data:image/svg+xml;base64,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","isTrigger":false,"operationName":"FilterToSPSDistinguishedName","operationDefinition":{"type":"Query","inputs":{"from":"@outputs('HTTPS_GET_GetMyProperties')?['body']?['d/UserProfileProperties/results']","where":"@equals(item()?['Key'], 'SPS-DistinguishedName')"},"runAfter":{"HTTPS_GET_GetMyProperties":["Succeeded"]},"description":"body('HTTPS_GET_GetMyProperties')?['body']?['d/UserProfileProperties/results']","metadata":{"operationMetadataId":"f88ef4d1-ef9a-45d8-8237-1df629d5e783"}}}
{"id":"0956922a-0427-4948-9fd2-e65cf0dd8e0e","brandColor":"#8C6CFF","connectionReferences":{"shared_sharepointonline_1":{"connection":{"id":"/providers/Microsoft.PowerApps/apis/shared_sharepointonline/connections/shared-sharepointonl-70a14524-6d74-4196-b1fc-31d350117f82"}}},"connectorDisplayName":"Data Operations","icon":"data:image/svg+xml;base64,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","isTrigger":false,"operationName":"FilterToSPSDistinguishedName","operationDefinition":{"type":"Query","inputs":{"from":"@outputs('HTTPS_GET_GetMyProperties')?['body']?['d/UserProfileProperties/results']","where":"@equals(item()?['Key'], 'SPS-DistinguishedName')"},"runAfter":{"HTTPS_GET_GetMyProperties":["Succeeded"]},"description":"body('HTTPS_GET_GetMyProperties')?['body']?['d/UserProfileProperties/results']","metadata":{"operationMetadataId":"f88ef4d1-ef9a-45d8-8237-1df629d5e783"}}}
TenantIdCNST
This Compose action is where you split() the string to get the value you need.

Use the following expression:
split(
split(
body('FilterToSPSDistinguishedName')[0]?['value'],
'OU='
)[1],
','
)[0]