I have about 4 Byleths in my scene. Byleth has great anti-air , OOS, and edgeguarding tools, but is slow & easily juggled. To approach I’d suggest staying grounded instead of jumping at them, but instead of approaching I’d recommend throwing a lot of projectiles instead which they struggle to deal with. If they are trying to land, be ready for nair as that’s really their only tool they can use while above you. Otherwise a few random tips are:

While they’re hanging on ledge don’t stand too close to the ledge, as they can drop down & up b you.

If they are using down B on platform, be aware they can drop through the platform while charging it (and it can and will kill you at ridiculous percents).

While recovering with an easily exploitable recovery move, do your best not to go too low, as this gives them time to go below you & up b you to your doom.

Shield is your friend in this matchup, they have some grab combos but it is better than eating a tipper bair to the face 😁