How to achieve SSR + SPA functionaly with a single app using vue3?

We are providing the option to create websites in VueJs to users from our CMS panel.
The rendering of these websites can be easily done using VueJs from CDN and achieve the SPA feature(routing without page reload). However some users want the SEO to work properly, and along with that, they want the application to run as a Single Page Application once the first page is rendered(using SSR).

NuxtJs would have been helpful if the applications were independently bundled but since we have a common rendering engine(NodeJs) and the views/logic are directly developed from the CMS panel( and stored in DB), things become complicated to achieve this feat using Vue SSR!

Is there any way to handle this for vuejs? Thanks!