I won’t tell you “it’s OK” to accept that certificate, as that’s a personal decision.
In Chrome, if you click the “Not Secure” area in the address bar
You can examine the certificate, including its trust chain, domains to which it applies, expiration date, … and make an informed decision.
To me, it appears that one of the Let’s Encrypt certs with their 90-day lifespans just expired.
Edit: As noted below, there is now a current cert in place.
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