ok, now had this confirm from TikTok…
Hi there,
Thank you for your patience while I was waiting for updates.
The reason that you do not see the option to sell your products from Shopify on Seller Center is that they are two separate platforms and we no longer support their integration.
I understand that this may sound confusing, however, I will give you some suggestions of what you can do.
Please go to your Seller Center account and upload the Catalogue manually. You can download your existing one as csv. file and upload it then onto Seller Center as an alternative.