You may be mistaken (about "aren't").
https://www.gov.uk/guidance/uk-trade-agreements-with-non-eu-countries-in-a-no-deal-brexit
Trade agreements that have been signed
Agreements with the following countries and trading blocs will take effect when the UK leaves the EU:
Mutual recognition agreements
Australia, New Zealand and United States have signed mutual recognition agreements.
Discussions with Japan on a UK-Japan MRA are ongoing. The UK and Japan have signed an exchange of letters designed to ensure the continuity of existing arrangements as a temporary measure.
A mutual recognition agreement is one in which countries recognise one another’s conformity assessments. When conformity assessments are applied to products, they are tested to an established performance standard. Inspections, quality management, surveillance, accreditation and declarations of conformity also take place."
You are right about Covid causing "mayhem"..... which may mean delays for practical reasons.
....but surely the evidence is that most non-EU countries want business-as-usual ?
And if formalities have not been signed between the UK and a.n.other country....
....does that mean that the Customs people in each country instantly demand "paperwork".
HMRC has already declared a "grace period" for EU imports - so (unless the country is very dodgy) why would we not do the same for a.n.other country ?
(I may be behind on the detail.....)
My understanding was that the French wanted a permanent fishing arrangement....
....while the UK had offered a 1 year deal (with rollovers).
Can we agree that "permanent" seems unreasonable as we don't know how fish stocks will look in the future .....
....but the UK could allow more years ?