[Portfolio] Long navigation menu

Hello, I have two portfolios: one by theme with a limited number of photos and a second organized by date and visited places.

For the second, there is a collection for each year, and a page for each date/place. For example, in the "2021" collection, there are 35 places visited, i.e. 35 rows that appear in the navigation menu, for this collection. I can also click on the collection to get the thumbnails (5 columns and 7 rows) .

I'm afraid that in a while it will become laborious to go down the page to consult the whole menu. How could I improve this point? Of course, I don't want to have a menu limited to collection names. Is it possible to have a scrollable menu, independent of the rest of the page, or can we expand or reduce each sub-menu?

Thank you.