i'm having the same issue and i tried running your solution it didn't work for me.
when i run npm run dev it gives Error: Cannot find module './v6/Model'
PS C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi> npm run dev
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\models\Model.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\services\models.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\annotations\AutoIncrement.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\index.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\src\sequelize.ts
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\src\server.ts
at Function.Module._resolveFilename (node:internal/modules/cjs/loader:956:15)
at Function.Module._load (node:internal/modules/cjs/loader:804:27)
at Module.require (node:internal/modules/cjs/loader:1028:19)
at require (node:internal/modules/cjs/helpers:102:18)
at Object. (C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\models\Model.js:6:13)
at Module._compile (node:internal/modules/cjs/loader:1126:14)
at Module._compile (C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\source-map-support\source-map-support.js:547:25)
at Module._extensions..js (node:internal/modules/cjs/loader:1180:10)
at Object.nodeDevHook [as .js] (C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\ts-node-dev\lib\hook.js:63:13)
at Module.load (node:internal/modules/cjs/loader:1004:32)
[ERROR] 16:10:09 Error: Cannot find module './v6/Model'
Require stack:
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\models\Model.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\services\models.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\lib\annotations\AutoIncrement.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\node_modules\sequelize-typescript\index.js
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\src\sequelize.ts
C:\Users\ADMIN\Documents\class exercise for udagram\dev\cloud-developer\course-02\exercises\udacity-c2-restapi\src\server.ts