is there a way to see in the schematic if a component is excluded from the BOM or board?
No. You can of course add some indicator yourself, but it doesn’t follow the changed attributes.
You can put a hash sign [Shift + 3] in front of the RefDes (a.k.a. "Reference in KiCad) to exclude it form both the BOM and the PCB, and this is visible on the schematic.
I think an icon on/next to the symbol would be beneficial and fairly straight forward to implement. Are there any arguments against creating a feature request on Gitlab for this? If no one can convince me this is a bad idea, I’ll do it
Sounds like a valid feature request.
It’s also a very logical feature request, and therefore it’s possible similar feature requests have already been made, and you have to search around a bit among the 1100 open issues.
For a feature request, it’s also advisable to thin about different ways to best implement the feature. For example, what about changing the background color for such symbols (You can already do that manually)
Maybe there already is an issue to list such items in a column in Eeschema / Tools / Edit Symbol Fields.
Just some wild idea’s, I am not in the mood to think this through at the moment.
Notice also that in the future it’s possible that assembly variants and layout variants will be implemented. They may be related to no bom / no footprint, respectively. See https://gitlab.com/kicad/code/kicad/-/issues/2131.
My first thought for spit-balling ideas for indicators to show the status of those checkboxes is some sort of icon or a strikethrough line on the related field. For the not on PCB switch use an icon or strikeout through the Ref’D, and for not on the BOM switch use an icon or strikeout through the Value.
To integrate with variants in the (distant) future, these indicators can be updated automatically depending on which variant is being displayed.
Just my (not fully thought out) idea.