Dell Latitude 5401 and 5500 microSD card details (fast ones)

Hi fellows, I'm grubbing the net - including all the available manuals and tech specifications -, and couldn't find an answer for my questions, which are: what type of microSD cards go to the microSD slot (I want to know the maximum-performance, trustful specifications: microSDHC, microSDXC (or SDUC), class 6, 10, or Ultra High Speed Class, e.g. UHS3), maximum capacity, and maybe a recommendation for the best brand (I'm on Ubuntu 20.04.01.). So, in a nutshell, t want to know the fastest microSD card's details which fit to my laptops. Thank you guys for the answers and for your experiences!!!

ps.: no, I don't want to compete with the SSD, just need a bit more (fast) space.