Hi @rigamuffin,
I hope you are well today and thank you for your question.
The 500—Internal Server Error occurs when the Web server (running the Web Site) encountered an unexpected condition that prevented it from fulfilling the request by the client for access to the requested URL.
Could you please check whether the solution posted on the following pages help you to fix this issue?
Also if you are facing the Parse error: syntax error on activating the theme then try using the solutions shared in the following topics.
https://colorlibsupport.com/t/parse-error-message-help/
https://colorlibsupport.com/t/shapely-on-wordpress-4-6/
Best Regards,
Movin