Well that's the point of the parent commenter though, right? How do you intend to support IE11 while using Bootstrap 5, even if the client offers to pay you?
If they really insist, they will be quoted a rewrite to another framework, plus more because we will hate to do that.
In practice we find solutions, such as installing chrome or using mobile devices. I know it depends on the domain and the country, but companies with outdated desktop pc running only internet explorer are becoming rare. We prefer to refuse one of them than wasting time supporting outdated environments.
