Here are the clubs who have debt that this Super League could have helped.
Spurs - Let's be clear, Tottenham were lucky to even be involved, they are not a big club in European football. However, the league was clearly built on the top 15 clubs in terms of current value... Spurs are in that group. Tottenham's new stadium is a sump on them because fans are not in it and they have yet to sell naming rights.
Real Madrid - This is a tricky one because Madrid has spent much of its recent history in debt, but it's often nonesense. I am not sure how deep into the sport people are here, but Real Madrid is known for always getting bailed out by the Spanish government, often in creative ways. The most famous example is the club selling its training ground to the government for a massive inflated price. The problem for the club is COVID increased the debt, while the pandemic alongside stircter financial rules in football and Spain's poor economy means the government cannot help. I personally think the government will step in eventually because Real Madrid is a thing of prestige for them.
Barcelona - These are in real trouble, a billion in debt and with no- way out. I think they still owe hundreds of millions in transfer fees for players who have been there years (Coutinho, Dembele, etc.) and have largely failed. What happens with Barca now is anyone's guess.
Italian clubs - I will group these together because they are in largely the same situation. AC Milan is slightly different because its debt is held on purpose for the American owners to take out dividends. Inter are being harmed by Chinese owners and new rules in China preventing spending on football. Juventus have been hit by COVID. All also have to contend with the lack of interest in Serie A, which means a lack of lucrative TV rights and low gates when fans can return. These clubs are in trouble, especially Inter Milan because they spend big two summers ago.
Chelsea and City - These clubs are not in debt simply because they have billionaire owners. Football fans have long prayed Abramovich would leave Chelsea, but always ignore that he has expressly said he will never leave the club in debt. He will pay off whatever debt the club has if he ever leaves. Also, the current debt is from transfers, I believe, which he writes off at the end of every season. Manchester City is in a similar situation with it's Middle Eastern owners, who have invested heavily into the club and Manchester to be fair. I don't know about their specific debt but I do know it will be written off by the owners.
Manchester United - United is unique in the football world because it's debt is not real. In fact, it is real but it is being held on purpose. United has been in debt since the Glazier family bought the club. Instead of paying the debt, the family takes out dividends. Manchester United is a money-making machine and could have paid that debt 5 times over during the Glazier's tenure. The owners choose not to do it to line their pockets. They pay the minimm debt repayment each year, admittedly spend on the team, and pocket the rest. United is perhaps the most self-sufficient sporting brand in the world if it was allowed to be.
Liverpool and Arsenal - Both these follow a similar path to United and the debt is kept on purpose so the owners can line their pockets.
Real Madrid has said the motive behind it joining the league was revenue and clearing debt, I would think Barca and the Italian clubs the same. But on the whole, this was not about debt but about ensuring that the money would be locked forever. They weren't going to pay the debt and then end the league. The American owners of the UK clubs wanted to create an NFL/NBA type league which guaranteed they would always get the top revenue. Chelsea and Man City it seems joined simply because they didn't want to be shut out of competing against the top clubs and the reason they pulled out so quickly is because they don't really care about the money involved.