For the 2024 US House of Representatives elections, the count of candidates is quite small. The three major third parties are running candidates, in their usual order by party size (count according to Ballot Access News):
Libertarian Party – 71 candidates
Green Party – 34 candidates
Constitution Party – 17 candidates
Other parties are running even fewer candidates.
In some states, there is really only one major party. In Massachusetts, of the 9 Congressional Districts, the Republican Party is contesting only two of them.
Green Party only had 9 US House candidates in 2022, so actually they did fairly well in 2024. Constitution Party also increased, because it had only 12 in 2022.
This information is from the print edition of Ballot Access News of Oct. 1, 2024. That issue has a chart listing the number of candidates for each party from each state. Republicans increased relative to 2022, and Democrats went down.