Chain ring and chain advice

Probably.
The chain length on the new bike should be optimised for the smaller chain ring.
If it's a full sus and you don't fit a longer chain you'll run the risk of knackering your mech if you don't check the chain growth under compression.

Cheers, will get a new chain also.

I'd check it rather than just buying a new one. Its only one full link different so the chain might accommodate a slightly bigger ring.

yep, some bike shops will sort the chain to the right length on building it, others will send it out with the full chain. Worth checking.

also - how worn is the 34T that you like, if that has started to wear then it might not mesh with the new chain anyway.

worth checking the new bike can accomodate the 34t, it probably should but quite a few bikes are now max chainring sizes although 34T is usually the upper limit.
it seems strange some bikes come with a 30T, my brother has a trek xcaliber and the gearing is ridiculously low even in his hilly surrounds.

ps. a 34T chainring on one bike may be alot easier in lower gears than a 34T on a bigger bike.

As above, I'd just check the chain length. It might be ok, it might not.

Would be a new 34t chain ring as it not a compatible with my current bike, also going from 27.5 to 29er

The change in wheel size increases the effective gearing. I'd be tempted to try the 30T for now and see if it is really too low geared.

Speak to the local bike shop to see if you can buy (or even be gifted) a few spare links. Nothing wrong with fitting a couple of quick links.

This guy even made a full chain from them 😂

EDIT: Notice at 6:17, he even has one upside down!

Have look at the gearing. A 29er 30x42 is 20.7 inches. A 27.5 34x42 is 22.3 inches.

So with the 30t on 29er your bottom gear is around 10% lower. Roughly one gear. Likewise your top end (with the same cassette) will be 10% lower.

https://galebernhardt.com/blogs/news/15198093-comparison-of-gear-inches-for-a-1x11-on-a-29er-and-27-5-mountain-bike.