Upgrading? Incremental or Big Bang ?

There are no particular advantages to upgrading incrementally. You may, for example, find that a particular app, system modification or workflow breaks upon upgrading from Catalina to Big Sur, or to anything later. That won't change the fact the app or workflow will need modification, updating or some similar inconvenience.

The one unequivocal necessity is the need to create a backup prior to upgrading, which Apple makes prominent mention of just about everywhere:

Back up your files with Time Machine on Mac - Apple Support

Depending on exactly what model Mac you have, you can potentially go all the way up to Sequoia.

The biggest issue is going to be compatibility with any existing apps you have.

Check your app compatibility before you upgrade.

Whenever you upgrade OS's this puts a lot of strain on the system. If you have an older Mac (2019 or older) then it likely has a spinning HD installed, the spinning HD is the achilles heal of older computers. They get a BIG workout when upgrading OS's, it would kind of be like putting an 80 year old man on a treadmill and having him run, meaning it's very stressful for the poor guy and anything could happen.

This being said, if you want to upgrade Mac OS, take it in 1 step to the latest version of Mac OS it will run. As we do not know the model year of your iMac we cannot tell you the latest version of Mac OS it will run.

HI there

Yes you can do like this as well, but I don't think it will make a difference. also check the app compatibility with some of the apps you are currently using and do wisely

Hope this Helps

Thanks