Well, I tried to connect to a paused M0 cluster using a MongoDB driver but this did not resume the cluster and failed with the following error:

Error: querySrv ENOTFOUND _mongodb._tcp.<...>.mongodb.net
    at QueryReqWrap.onresolve [as oncomplete] (node:internal/dns/promises:240:17) {
  errno: undefined,
  code: 'ENOTFOUND',
  syscall: 'querySrv',
  hostname: '_mongodb._tcp.<...>.mongodb.net'

From this stack overflow post javascript - Error: querySrv ENOTFOUND _mongodb._tcp.dbname.fzofb.mongodb.net - Stack Overflow it looks like this error is expected when the cluster is paused.