Use USB attached SD card in gallery

When traveling I usually only have my tablet (Samsung Galaxy Tab S8+) with me but not a real PC. So to have a quick check of the pictures I took during the day with my DSLR camera I'd love to use the big tablet screen (or even the hotel TV connected with HDMI) and not the small camera display. So I got myself an USB-C "dock" that can read SD Cards (and also output HDMI). Using the Samsung file viewer I can now see the internal storage, the SD Card (which is the micro SD in the tablet internal reader) and also "USB storage" - which is exactly the SD card from my DSLR that I want to view. So everything could be fine. But no gallery app that I tried could access the "USB storage". The only thing that worked was to open an individual picture by selecting it in the Samsung File app and then choosing the picture viewing app. But even in this case the viewing app couldn't open any other picture of the USB attached SD card by itself. What possibilities do I have to view my pictures in such a setting where the SD card is in a card reader connected by USB?