If you don't want to manually add the CA cert, and want to wait for the update from MikroTik, you can change the DoH URL to https://mozilla.cloudflare-dns.com/dns-query. It's still Cloudflare, but with better privacy/less data collection. It's the URL used by Firefox when you select Cloudflare as DoH provider in the browser.
This URL still uses a certificate with GlobalSign Root CA as CA and the cert is still valid until April 7th (it was renewed last week).