I’m envisaging switching from Vercel to Render for a multi tenant NextJS app because of their 50 domains per project limit and overall bandwith pricing, do render have such limits ? If not are users still forcibly limited Let’s encrypt’s 100 names per certificate limit ? Rate Limits - Let's Encrypt
There’s currently no limit of custom domains on services, however, there is a charge of $0.60 per custom domain after the first 25, as noted in the docs here: Domain Names
The Let’s Encrypt docs you shared refers to a 100 domain limit on SAN certificates (multiple domains on one cert), which isn’t a limitation only with Let’s Encrypt. Render issues a single certificate per custom domain and mostly utilises Cloudflare certs.
Render does also have bandwidth charges, mentioned on the Pricing page:
Each service is allowed up to 100 GB/month in egress bandwidth (network traffic sent by your code). Usage above that is charged at $0.10/GB. Ingress bandwidth (network traffic received by your code) is always free.