Who benefits from high voter turnout? And by how much? This is an unsettled debate.

"Why Donald Trump should be hoping for high voter turnout"

Take a look at a New York Times/Siena College poll released earlier this month. Trump had a 2 point advantage among registered voters. Biden was up 2 points among likely voters... This would be quite the shift from what had 

. Normally, Republicans gain about 2 points when going from registered to likely voters.

"Voter frustration could be key to turnout in 2024, experts say"

Republican strategist Charlie Kolean... said he believes a lower-turnout election would likely benefit Trump more than Biden. Kolean argued that many in 2020 were voting more so against Trump than for Biden, and less enthusiasm exists for Biden now.

 covering the alternate case ("low turnout") to estimate the impact of turnout on the election outcome. 

[1]. The goal isn't truly "record" turnout. Rather, the population is growing, but most people expect the proportion who vote to decrease as well, so "record number of votes cast" seems like a reasonable threshold for "higher" versus "lower" turnout.