How I can organize my photos to make it easy to find these fastest?

38K is not a large library these days, and as you don't say how you're searching, and how long it takes you to find images, it's impossible to do more than a quick survey of the possibilities Photos offers.

At heart Photos is a database, and to coin an old joke, a database is a like a sewer, what you get out of it depends on what you put into it. So the more effort you put into categorising your images the easier they will be to find. Some things are done automatically: date and time, for instance, so easy to find if you know when the photo was taken. The Places feature, if your camera device tracks that data, means you can find all the images taken in London, or Spain or New York. If your camera doesn’t track that then you can add it in manually. If you're looking for a particular person then the more time you spend naming people in the People section the easier it gets. The AI feature is also useful as it categorises images by what it can recognise in them, so search for 'trees' or 'mountain' and it will find any images that contain these features. Then there is the keywording feature which allows you to further categorise the image using any system you can devise.

As well as the search box you can also create Smart Albums to find images - like all the Photos of John taken in New York in September last year, and even limit those to one you favourited or are work and not holiday images...

So basically, Photos offers you Who, What, Where, and When, as well as any other categorising feature your can devise to help you find your images.

Perhaps this user tip can help a bit - I wrote it for Photos 5, but is still valid for Photos 7: New to Photos? Some Considerations on How to design your Photos Library… - Apple Community

You may want to look particularly at the second part, where I am describing some ideas to add a thematic structure to the photos library using albums, folders, keywords.

Since you haven't told us what you are looking for, it is kind of hard to tell you how to find them.

One thing to try in the new Photos that Leonie might not have mentioned, is that the content aware search can work pretty well. So you can try to search for "dogs", "trains" or "bridges".