I don't know, I don't think I've encountered any WASM app. Chromium is generally slow on the PinePhone, I would highly recommend Firefox on Phosh (unusable on Plasma unfortunately if this hasn't been fixed). Gnome Web and Angelfish (KDE's mobile browser) work well too.

I would not seek for WASM apps though. Those generally require big and heavy runtimes to be loaded in the browser for questionable benefits, with no way of sharing those runtimes with other apps. I would rather look for native apps, or Web apps with lightweight frontends which can actually be quite fast if done well.