Hey! Welcome to our forum.
First off, Riseup is not meant to be used as a privacy-conscious email provider for regular use. Unless you are a journalist or activist that is seeking a safe work-related email address, you will only encounter usability issues associated with smaller nonprofit providers like Riseup that lack the resources of a company. If you need request an invite code online, most likely, you are not the type of person to utilize Riseup.
If this threat model applies to you, I recommend reaching out to your network of journalists or activists for an invite code. Otherwise, we recommend established providers such as Proton and Tuta for daily use.
Please refer to this previous topic on the subject for more details.