Using the Modbus binding, you can configure Things and channels manually. You will need a detailed knowledge of the target devices modbus register map.
Some of the posts show you that. Very often they show you using xxx.things files, because some of us prefer managing Things that way for modbus.
But it’s not hard to read those, and use to set Things and channels using MainUI instead.
Overall though, this is hard work if you do not know exactly what you are doing.
Some devices offer self-identifying or ‘discovery’ features - they announce what they can do. It’s not completely hands-off, you have to do some basic configuring. A common standard used by inverters is “SunSpec”. SMA devices do offer that.
See