Looks like bacterial wilt spread by the cucumber beetle. Other possibility is squash vine borer,

Thank you both. Anything I can do about this situation at this stage, to at least allow for maturing of already half decent sized fruit ?

The insect is a squash bug. They don't transmit diseases like cucumber beetles do, but they can do a lot of mechanical damage to squash plants just by feeding: https://extension.umn.edu/fruit-and-vegetable-insects/squash-bugs

It looks like you probably have combination of pathogenic issues (from cucumber beetles) and feeding damage from the squash bugs.

Unfortunately, if it is bacterial wilt spread by cucumber beetles, there is no cure. You have to keep the beetles off the plants in the first place.

In the pictures, I really don't see any squash bug damage, but you certainly have an incipient problem if they're around. As noted, no clear remedy for bacterial wilt, though removing the affected leaves at least may help prevent spread. You might plan on planting something else there next year. Early doses of pesticide are often an effective preventative.

Although bacterial wilt is possible, I suspect the problem is early stage squash vine borer (SVB) damage. Such wilting often begins with leaves wilting late in the day, then recovering overnight. Damage typically begins to show about this point in the season, and will gradually increase. You can identify SVB infestation my examining the lower stem, looking for cankers with "frass" (similar to sawdust) expelled from the holes.

SVB attacked my Buttercup squash several years ago. I was able to save the plants by burying the stems so additional roots would form, and flushing out & killing many of the larvae using a water pick. Just be aware that if what you have is SVB, some of the larvae will drop, burrow underground, and pupate over winter. The adult moths will emerge next year... as they did where my Buttercups had been previously.

The insect in the photo is a squash bug. Those too are damaging, especially if they have multiplied to large numbers. If you see a lot of those (and their grayish nymphs) and there is no sign of frass, they could be causing the wilt. Although I have SVB in my area, it was squash bugs which killed my squashes last year.

Regardless of whether the wilt is caused by disease or insects, I would recommend not planting squash in that same location next year. Any dead plants should be burned or disposed of.

Its out first year in the country with big gardens and planting many things incl. squash. So far we have been faced first with rabbits, cucumber beetles, Japanese beetles, earwigs, squash bugs, and hornets. Just saw a big grasshopper in the lettuce patch....

The beans and zucchini are still small, more experiences ahead. Since both the cucumber beetles and Japanese beetles are all over our property, I can't see us planting squash next year. So far we have been doing well with garlic, lettuce, spinach, kale, and tomatoes. Will stick to those...

I just wanted to add that I used to have lots of squash bug, etc., problems on my butternut squash, but after I went to trellising it, I really haven't had a problem. I also noticed that they would destroy my zucchini. I moved the zucchini out of my garden to a different location, and it helped the butternut squash too.