Hi @TomHughes ,
Do you want to save multiple selections from Forms to SharePoint list?
I have made the following flow for your scenario, please check it for a reference.
Add the trigger When a new response is submitted. In the form, I have a multiple selections enabled field.
Initialize variable, set its Name as Test, Type as Array.
Get response details. An Apply to each will be added automatically after you select the response Id.
Add a Compose action to remove all the special characters:
replace(replace(replace(body('Get_response_details')?['rb12b59186b54449d83e54595ebe4eb10'],'","','|'), '["',''), '"]','')
Add a Compose 2 action to split the previous output into an array:
split(outputs('Compose'),'|')
Add an Apply to each 2, select value from compose 2 output, add the action Append to array. Here, set its name as Test, Value as dynamic content Current item of Apply to each 2.
Under the Apply to each 2, add Compose 3 with the following code:
join(variables('Test'),',')
Add the action Create item to add the output of Compose 3 to corresponding column.
Images for your reference.


Best regards,
Mabel