Standalone application can't be opened OSX 12.3.1 Max 8.6.0

Going a little around in circles - from forum posts to old knowledge.

I've managed to build apps in the past from Max for OSX and load them on other machines. Most recently for a 2 year install - on an intel mini - and all was fine.

Today I've just finished an OSC based app on a M1 MBP OSX 12.7.
Really, pretty simple app. Built the app and tested on the same machine, and all works great.

Copy it to an M1 mini OSX 12.3.1 and get the dreaded note :

The application "OSC Remote Control V0.9" can't be opened. OK.

No other information. Tried all sorts of ways of opening it with no dice.

I realise there are just so many variables when doing this, and I'm likely missing something pretty basic (thus tagging as beginner - but have enough experience to think this shouldn't be too hard....)

I've tried reading as many forum posts as possible about it - and one came pretty close, but there was no resolution that I found.

I don't think its gatekeeper (or is it?!)

Is there an up to date (OSX 12 or above, Max 8 or above) guide to creating standalone MAX apps for OSX around that I've not found? Or can anyone offer any suggestions as to what things I should try?

In the end, this little app will run on 4 different macs (all M1's and M2's - minis / studios).

I'm going to keep trying - but I feel like I'm flailing in the wind.