To get into more details and confirm (sorry):
1. Manual trigger undoubtfully falls into the category of "manual" triggers, and hence will use initiating user's identity/access/permissions/license for the flow and all connectors inside the flow. It is possible however to change this for each connector inside the flow and run a specific connection under a different account (take advantage of the owner's premium license). Correct?
2. Selected SharePoint item trigger: flow runs under initiating user's identity/access/permissions/license for the flow and all connectors inside the flow. It is NOT possible to change identity used for a connector inside the flow. Correct?
3. Everything else (it seems to be) falls into the category of automated or schedule flows, and hence run with the identity of the "creator"/owner, which can be changed ONLY if flow is in a solution. Seems like it's better be, right?
Also, it seems like only the current owner needs a premium license for premium connectors to be used in the flow, and it is not needed for the initiators. Is this correct?
4. There is one more type I can think about which is a manual flow triggered from the Power App. I believe this one runs under the account of a "creator"/owner (despite being manual) but initiator MUST have appropriate license to all connectors used. Is this correct?