From here your DNS looks right: NS ns1.reg.ru / ns2.reg.ru, four apex A records on the GitHub Pages IPs, www → genpauls88-gif.github.io, no CAA / AAAA / DS. HTTP already returns 200 with Server: GitHub.com. The Pages API for genpauls88-gif/stalnoy shows the custom domain set but https_certificate: null, which matches a DNS check that never finishes — provisioning has not started yet.

Direct queries to the authoritative nameservers time out:

dig @194.58.117.17 stalnoykontur.ru CAA   # ns1.reg.ru → timed out
dig @194.58.117.16 stalnoykontur.ru CAA   # ns2.reg.ru → timed out

Public resolvers answer fine; GitHub's Pages checker often fails on CAA against these nameservers. Same pattern as #208857, #209098, #209317 and #208881 this week.

Workaround that got a certificate issued today on another .ru domain (#208857): leave REG.RU as registrar, move DNS hosting to Cloudflare (free, records set to DNS only — not proxied), recreate the four A records + www CNAME, wait until dig NS stalnoykontur.ru shows the Cloudflare nameservers, then remove and re-add the custom domain once in Settings → Pages. Leave it alone until Enforce HTTPS unlocks; if it is still stuck after ~24h, open a ticket at https://support.github.com/contact with the health/Pages API output.

(Side note: public DNS already has www → genpauls88-gif.github.io — one "s" — which matches the Pages account. Keep that target.)

Based on the configuration you posted, the four A records are correct and the www CNAME is also in the correct form. GitHub's current documentation lists exactly those four IPv4 addresses for an apex GitHub Pages domain.

The important clue is that “DNS check in progress” has remained for several days. GitHub says DNS changes can take up to 24 hours, and HTTPS provisioning normally starts after the DNS check succeeds. Several days is therefore not normal propagation delay