I'm new to Altium. I have a question about libraries in Altium. If I draw a passive component such as a capacitor in the schematic library of Altium, after all packages of capacitors like 0402, 0603, 1206, and so on separately draw their footprint in PCB Library. Is it suitable to add all footprints into a component symbol in the schematic library of Altium?
You can do this, and it's fine if you're doing assembly yourself, but it's not the convention within Altium and it makes getting professional assembly done more complicated.
On the upside, it means you can just make one generic resistor and set its value and pick the right footprint each time you want to add it to a design, without needing to worry about any extra work creating new schematic symbols for each manufacturer part.
However, when you export the bill of materials (BoM) and pick and place files for manufacturing, the generic resistor or capacitor that you've chosen will be exported without an associated part number, so it won't match up with the actual parts you need to order and have assembled. You'll have to manually do all the data entry to make sure the right parts get assigned to the right component designators.
What I do is create schematic library entries for each of the manufacturer part numbers you want to use (you can copy-paste the actual symbol graphics and pins) and then assign the correct footprint for that part. That way, when I export the BoM and assembly documents, I know everything is correct. Since I fill out parametric data for my parts, too, I can quickly find real parts that I know will fit my needs.
You can also use the Manufacturer Part Search to pull information from suppliers, including parametric data and stock information, and import a specific part as its own schematic library item.
If you happen to be using JLCPCB for your designs and assemblies, I auto-generated Altium schematic libraries for all their passives, complete with parametrics, so you can save yourself a lot of time and effort there.
It's up to you. If you want each component in the library to represent a specific component with one or two possible part numbers and suppliers then it doesn't make sense to have multiple footprints.
If you just want a generic capacitor symbol and you'll figure out the BOM part number and suppliers some other time, then your method involves less up-front work (and more work later).
Similarly, you can create different symbols for each value (as well as package) of capacitor or resistor or just have a generic 0402 or whatever. At the extreme you can create a 3D STEP model with value markings for (say) each 0603 resistor and tie that to the component package and value.
Some suppliers such as JLC may make a subset of their available components available as an Altium library, which simplifies ordering PCBA from that one supplier.