I'm new to Sharepoint Online (and SharePoint in general) and have a question about external sharing. I would like to create a form that would need to be filled out by multiple different users and use a workflow to route the form to said users. However, one group of these users is an external group who need to simply give their approval. I understand that I cannot share an InfoPath form with external users. Is there any other solution I may be able to use?
Since InfoPath Forms Services are only supported in Office 365 Enterprise E3 plans or higher, if external users want to access InfoPath forms, they need to login with credentials. More information you can check in the article:
There is a workaround which use Word and email to external users, check if it’s feasible for you:
Create content type with relevant columns which you want external users filled in.
Create a word document and use quick parts to insert the columns to the file.
Use word email feature to send the file to external users and external users email back after filling the file.
More detailed steps check the post: External Form Submit to SharePoint