An important thing to realize about Congressional districts like this is that because the ratio of Hispanic (and other minority) population is already so lopsided towards Hispanics, it doesn't take much of an absolute decline in the white population (or voter) share to lead to a pretty large increase in the ratio of Hispanic population. For example, if the white population share drops from 22% to 20%, that is only an absolute drop of 2% of the population (and also only a 9% proportional decrease in the white population share.
But it increases the ratio of non-white to white population from 3.54 to 1 all the way up to 4 to 1, a 12.8% proportional increase. 12.8% is significantly larger than 9%, and certainly more so than 2% (which might have seemed negligible to a naive view).
And it is the ratio of population that will be reflected in racial vote share (depending on turnout).
Similar logic also applies to turnout. If Hispanic turnout increases, it may actually end up netting Biden more votes, even if it is also true that Trump earns a larger share of the increased Hispanic vote.
So as a result of this, even if Trump does make some decent gains in his share of the Hispanic vote that you might think would result in him winning this sort of district, that may not necessarily be the case as a result of the general long term overall continuing trend of increasing Hispanic/non-white population (and voter) share, - provided at least that Biden continues to win Hispanic voters overall and the magnitude of Trump's Hispanic gains are not too large.
That is all the more true if Biden does relatively well among white voters (though that is open to question, a lot of the national polls that show Trump gains with minority voters have also showed Biden doing well and even making gains among white voters, so if you believe the one, you should probably also believe the other as well).
This is a good analysis - one thing I would add is while CA-13 is 65% Hispanic and 22% white as of the 2020 census, in practice, Hispanics may only be a plurality of voters and whites nearly 40% of voters in a normal cycle.
These central valley seats are interesting because they have some of the worst turnout in the Country, and in midterms, even midterms where Democrats are doing well nationally, Democrats always seem to struggle in these seats because of the Hispanic vote dropping off. I think another thing that's not helpful for Democrats is in seats like CA-13 you don't have a significant high-turnout college educated white base - even if white voters are swinging towards Biden nationally, if that swing is disproportionately amongst college educated whites it may not help Biden much here.
If I had to guess, Biden does a bit worse here than 2020 but Trump doesn't flip the district.
