Yeah, last season was shit, probably his worst season. But that's wasn't his usual season, so I wouldn't make decision just based on last season.
He has already shown what he is capable of in multiple seasons (his first season and 2019-20 was very good, 2017-18, 2018-19 was good, 2015-16 and 2020-21 was poor).
If we have someone like Haaland lined up, then yes we can sell him. Not without any replacements, Greenwood is not ready to lead the line, Cavani is not young player. So we shouldn't be trimming the options.