Cuba Sanctions - United States Department of StateCuba:...

Cuba Sanctions - United States Department of State
Cuba: Helm-Burton Act (state.gov)

Disregarding refineries, two webinars back, AP was indeed questioned about this. The question had been phrased as 'should US-Cuba normalise relationships, what is the risk for legal action on block 9' - or words to that effect. The implication being the Helms-Burton Act.

MAY's response was that they had investigated, and in-ground resources were always the sovereign property of Cuba and that they did not believe it would be an issue.

There have already been failed attempts to sue using the act, including one concerning harbour infrastructure used by cruise ships.

Two Years of Title III: Helms-Burton Lawsuits Continue to Face Legal Obstacles | Advisories | Arnold & Porter (arnoldporter.com)
The Helms-Burton Act Backfires: Surprising Litigation Trends Following Title III’s Long- Feared Activation by Gergana Sivrieva :: SSRN

The relevant Title III of the act can also be, as has been on numerous occasions, suspended by the US President in the interest of US-Cuban relations.

Relations between the US and Cuba were beginning to normalise from 2015 when Obama visited Cuba; this was later undone by Trump's National Security Presidential Memorandum (2017-20-10).

Obama Cuba visit sets new tone - BBC News
Federal Register :: Strengthening the Policy of the United States Toward Cuba

Sherritt has/had a claim over its nickel / cobalt project for some $80+m (at one time exceeding its market cap). Also, because of the Act, Sherritt's CEO is unable to travel to the US (curious to know if this is the case for MAY senior management). Canada clearly thinks its all a crock.

Donald Trump's tightening of Cuba policy pushes Canadian miner Sherritt to the brink | Financial Post
The Impact of the Helms-Burton Act on Canadian Companies Operating in Cuba - HillNotes

A stroke of a pen by Biden could sort it out (for a period).