Most cheap simple cassette recorders will work fine. But avoid old ones, dried out belts are common.
Most digital ones will also work fine, Nils used one?
A PC with (USB) audio in/out is what I use if ever I use audio, which is rare.
MP3 might work, if compression is not set too aggressive.
But I have not used audio recordings since the last time I digitized my cassette collection in 2004, all in uncompressed wave files on the hard disk of my computer. The KIMtape DOS utility can read and write those wave files.
At that time my computer controlled audio cassette desks, not used in 15 years, turned out to be garbage (completely crumbled belts and wheels) and I used an old simple cassette recorder to save the files.
I did adjust the head of the recorder (with the little screw hole next to it) for optimal pitch while playing old recordings. This is a thing to check if this is available when buying a recorder!