Strings Playback In Versions of MS

This is much less a matter of the MuseScore version than one of the soundfont being used.
And there actually MuseScore 3 has the better one by default, and with the HQ extension yet a better option, esp. for strings (but for 'Save online' you'd need to upload the score audio as well, like always when using a non-default soundfont)

Older version of MuseScore can get obtained from https://musescore.org/en/download#Older-and-unsupported-versions
You can get other soundfonmts from https://musescore.org/en/handbook/3/soundfonts-and-sfz-files#gm_soundfo…, including those from MuseScore 2.x

You wrote:
in MS 2+ The strings, especially violins and violas is much better in my opinion. It seems more defined.

You can obtain the MuseScore 2 soundfont from here:
https://musescore.org/en/handbook/3/soundfonts-and-sfz-files#gm_soundfo…
and use it in MuseScore 3

Also see:
https://musescore.org/en/handbook/3/soundfonts-and-sfz-files#install

Although there were changes to the soundfont between MuseScore 2 and 3, they were not that large, and most strings are essentially the same as far as I know. But, do be sure you really are using the same sounds. MuseScore provides both "slow" and "fast" string sounds as well as "normal" ones, and they are optimized for different types of music. The slow sounds sound good for whole notes etc, with a little crescendo into each note (played with a slow bow attack, hence the name) but are pretty much useful for passages involving sixteenth notes etc. This was equally true in MuseScore 2, but I'm not sure what you mean about choosing "orchestral" - that has never been the name of any string sound in MuseScore. You are still wlecome to try the various different sounbds that are available, juyst as you were in MuseScore 2. Nothing has changed in that respect. So pehrpas you had loaded a different soundfont? If so, you can do the same in MuseScore 3. but keep in mind, others won't have that same soundfont, so if your goal is to share with others, best to choose one of the standard sounds.

I'm not sure if it's still possible to upload MuseScore 2 files or not, but if the poiint of sharing the files is to make them available to others, I wouldn't do try to do that in the first, place, as virtually everyone else in the world is using MuseScore 3 (and sooner MuseScore 4), so when they load your score, it will doubtless look and sound different. It's always best to optimzie your score for current versions of MsueScore if you wish to share with others.