Is the transfer from Origin to EA app fully smooth yet?

Hello!

I was playing on Origin offline for several years.
Then after migrating to a newer PC i updated my Sims 4 and my origin in 2022 april. Without exaggeration it took me several weeks to fix the issues that the updates caused to my game, and had to live with some as i was unable to figure out a fix for them, so i turned back to fully offline gaming.

Now i keep reading and hearing about how Origin shut down in october last year, and after much research on the topic i have yet to come across a single positive feedback about the new EA app.

I would like to purchase some Sims 4 packs from the Spring Sale that are compatible with my current game version, as i decided i will not update my game anymore, even if it means i cannot buy or try the latest packs.

What i would like to know, is how am i able to transfer to the EA app, purchase some packs that are compatible with my current game version, download and install them without updating my Sims 4 to the latest patch, and then, will i be able to go into a fully offline mode, that doesnt require being online even for a moment? 

Thanks in advance for reply!

EDIT: Also curious about how the new app handles mods, as i have come across mentions where locally saved gallery items and mods vanished and i have not heard back from them if they were able to solve the issue.