TL;DR -> Yes you will risk it if you don't perform a proper audit and migration from the original platform.

Any type of architecture changes can 100% ruin your SEO if you are not migrating content and topics correctly. Many people assume this is limited to URI structure but underestimate the power of Topical hierarchy and the content, internal linking and URI structure which play a crucial role into any migration effort.

If you have any questions about the migration process, give me a shout.

Decent free migration checklist: https://searchengineland.com/site-migration-seo-checklist-dont-lose-traffic-286880