Suffix show border radius-left to the field group
The radius comes from .input-group-text. Aside .input-group-append class used here is a breaking change in bootstrap 5 per https://getbootstrap.com/docs/5.0/migration/#forms
.input-group-text
.input-group-append
Fixed
5.0
Code
Issue #3474503: Prefix/Suffix show border-radius attached to field
Can confirm ist works.
But why have you removed field-prefix/suffix? It may be a helpful class to address the span if someone may needs to customize it.