How do I start troubleshooting an "I - invalid" configuration?

I recently purchases my first RouterOS-based product, and I’m experimenting with the settings. Often, after I’ve configured something it will show an “I” next to it in both the console and the GUI. Tooltip in the GUI and legend in the console say it means “invalid”. I can’t seem to find a place in the GUI or console which elaborates on why any given setting is invalid. Where can I get that kind of information?

I’m intentionally not providing my current configuration because I don’t want people getting tunnel-vision. I am asking a very general question because I need the general answer. It’s important for me to be able to do at least a little troubleshooting on my own rather than needing to make a forum post for every issue.

A good place to start looking would be system logs … not everything is recorded, but something might pop up. But my experience is that there isn’t a single way to troubleshoot configuration problems and one often has to deduct the problems.

You gave us almost no information to go on. As mkx said, the logs MIGHT help, but don’t count on it - a lot of stuff is not logged unless you tell it to be. Since you gave us no information to go on, about all I can suggest is to read the docs for the command or setting you are getting the invalid indication on.

So RouterOS doesn’t provide any kind of error code or error message? Just “Your setting is so profoundly wrong that I can’t even try to use it, but I’m not going to say how I know that”? I find that absurd.

Generally ROS doesn’t accept configuration stanza which is profoundly broken. But then there are configuration stanzas which are syntactically correct but don’t make sense in current context of overall configuration.

The thing is that with ROS one can do many things that are not really possible with other routers in the same price tag (that’s specially true for the SOHO line of devices). It is almost impossible for ROS command parser to determine correctness with 100% accuracy … before operation fails. Many of Mikrotik users prefer versatility of ROS over being foolproof and accept the fact it’s harder to troubleshoot. But then versatility of configuration inevitably comes with versatility of troubleshooting. And ROS provides a few quite powerful tools to do that too. One just has to master ROS enough to know where to start troubleshooting.

As previous posters said: it’s hard to point you in the right direction without you providing any context. But you declared you don’t want to for perfectly valid reasons and I respect that.

“I” flag is so generic, that there is no way to give any pointers, without knowing the menu you are in. For each section it can be something else. Often it’s relying on something that is not active or enabled.

https://help.mikrotik.com/docs/display/ROS/Getting+started is a starting point but there are things stated that I dont particularly advise but its overall pretty good.

ROS = stick with defaults for beginner
ROS= dont experiment if you dont have a clue
ROS= use safe mode to make changes
ROS= get some literature
(https://www.amazon.ca/Routeros-Example-2nd-Stephen-Discher/dp/0692777903/ref=sr_1_1?dchild=1&keywords=discher+learn+router+os&qid=1625744161&sr=8-1)

Use more credible sources on youtube, there are many that are plain bad and many are very tailored to specific scenarios.
These seem okay to me.
(https://www.youtube.com/watch?v=76nK1LXyPMA&t=9s series)
(https://www.youtube.com/watch?v=OXZAXPZce4U&t=445s series)
(https://www.youtube.com/channel/UChAnP0FHKtlj_BypECp-40w )

When looking for help the following three items will get you the best responses…
a. network diagram
b. copy of config (complete) /export hide-sensitive file=anynameyouwish
c. the most important of all - a clear set of requirements - what you want your users/devices to be able to do or not do without any mention of the config or solutions.

Are those YouTube links examples of credible sources or bad sources?

Better than most LOL.
There isnt enough space to list all the bad ones …