One stumbling block to claims of voter fraud in the 2020 election is the large number of court rulings against lawsuits making such claims. Some proponents of these theories have tried to argue that no judges actually examined the merits of these claims, but this is false.
A recent RedState article by Stu Cvrk takes a different tack, arguing that Trump and his allies actually won many election lawsuits. It points to an interesting database of such lawsuits.
2020 US Presidential Election Related Lawsuits
The article and database try to spin the results as favorably for Trump as possible, but they omit a few pertinent observations. Most of the wins are in the category of "rules", one in "process", and one "miscellaneous". None of the wins involve vote counting machines or other voter fraud.
Changes to election laws and policies that occurred shortly before the election are a legitimate issue, though often overstated. Many of these changes were reversed prior to the election.
All but one of the wins in cases filed by Trump and his allies occurred before the election or the next day. Only one occurred later. The time to challenge these changes was before the election, not after. Overturning the election based on policies that weren't challenged before the election was never going to happen.