Trump is not as worried about winning as he is exposing the corruption that is the Deep State/Democrat Party.
If he files lawsuits, he can depose leaders of the various states. Under Oath.
If he can get enough evidence that there were irregularities and fraud, regardless of the number of votes proven to be fraudulent, it throws the election result into doubt. If enough doubt is generated, the Supreme Court could very possibly decide that the election was not held in a proper way. If they invalidate the results, then the election is given to Congress to decide. if that happens, Trump wins (House selects President, Senate selects VP).
Example: If I find a rat in my can of food, and the packing company argues there's no evidence showing a rat getting into that specific can of beans, then it's up to me to prove that it's POSSIBLE that the rat was put in the can at that plant.
I only need to show that the PROCESS on the canning machine line offers the OPPORTUNITY for a rat to make its way into the canning machine. I could be trying to scam the company for a payday, so they are not going to settle if they think there's no way the animal made it there.
Just like that scenario, Trump doesn't have to prove that X number of ballots that he lost by were fraudulent. He just has to place enough doubt on the process to prove it was POSSIBLE for fraud to occur. There are stories of thousands of fraudulent acts at all levels of the process as well as improper security and deliberate lack of transparency across several states. These proven instances of fraud prove there was an OPPORTUNITY for someone to commit fraud -- POSSIBLY to the degree that it could have changed the outcome.
If Trump is 10K ballots behind, that does NOT prove there were 10K+ extra Biden ballots. But if the process was not controlled, it does prove that there could have been 5K illegal ballots for Biden, and another 5K+ Trump ballots that might have gone missing. When you add ballots without tossing a similar number, the vote totals become red flags. If you get 10K ballots from a precinct of 8K registered voters -- that MIGHT be a problem!