@Anonymous yep, that's right, based on what you said previously I don't think you need to worry about the 5k limit. But it depends on your filters. What I said is if you filter for created items and you run your flow daily, if you'll never have more than 5k items created per day, no need to spend time on developing a flow that could handle such scenario.
As for indexing, yes, the columns you'd like to filter on in the list must be indexed, but again, if you fail to create your own indexes, SharePoint will do that automatically for you. Although I always suggest you do them because you know your data better than a script.
About those solutions to get more than 5k in a flow, well, it's always best to avoid it if possible. There isn't one perfect solution, but one that fits your requirements best. Generally, I'd say, only look at such an option for running non critical service flows usually with overnight execution..
That said, if you really need it, querying the lowest and highest Id for which the filter returns results and looping through in increments is usually a solid implementation: https://tachytelic.net/2020/12/power-automate-sharepoint-5000-items-easy/
Hope that answers your questions