Codec settings for generic device

I work at a public library and we created videos of our library children that we want to display on a generic digital picture frame that supports video. I made the original videos in Windows Movie Maker and then used an on-line converter to convert to an MP4. The limited information I got with the digital picture frame says that it will support MPEG1, MPEG2, AVI, MP4 video files, with the only disclaimer being that "Video files may not play if stored on a low speed (SD) card". I purchased a SanDisk Extreme Plus 80 MB/s SD card and I know that the digital picture frame recognizes it. That's when after searching on-line I learned that the codecs may need to be converted. I have tried several free download codec converters and tried to create new files. I have been successful in creating new files, but alas, I still cannot come up with a file that will play on my digital picture frame. Part of my problem (I think) is that there are SO MANY variables in these converters and I have no clue what a lot of the settings even mean. The file sizes that I am working with range anywhere between 12 MB and 324 MB. Could I get some advise on anything I could do or settings that I should be paying attention to to get my videos to play on my generic digital picture frame? Many thanks in advance!

Here is a simple and free offline converter:
https://handbrake.fr/

Use these setting:
Preset > Regular > Normal

This will create a MP4 file with H.264 video and AAC audio. If you don't need audio, then on the "Audio" tab, press the "Clear" button.

On the "Video" tab you can find an option called "Constant Quality". This value controls the size/quality. Try value 24. Lower it if quality is not good enough. Increase it if quality is more than good enough, but you want smaller filesize.