Manjaro being a rolling release, theoretically you should be able to install it once and never again do a reinstall, at least as long as there are no catastrophic problems. However, every so often I hear someone on YouTube say it is healthy to do a fresh reinstall every so often.
Some people here haven’t reinstalled their OS in years without issues.
Though some people like to reinstall Manjaro to get the newest configurations setups, as updating your computer doesn’t change to the setups the maintainers make in ongoing changes.
And every so often I see decent advice coming from a youtube video. But its very rare.
I suggest not relying on that ‘source’ and instead use things like the arch and manjaro wikis.