Importing backup from older laptop-

deckstatic wrote:

I'm upgrading from my 2018 Macbook pro to the newest model; if I backup the old one to an external drive & then import it as a backup to the newer one, will there be any issues? thanks!

You are better off starting a new Backup for your new Mac to avoid complications.

If your new Mac inherits your backup history - Apple Support

https://support.apple.com/guide/mac-help/if-your-new-mac-inherits-your-backup-history-mh35732/mac

Time Machine is great when it works, not so much when it doesn't...

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

deckstatic wrote:

I only use an external drive (with a backup one for that). So will "Migration assistant" work for this process? My main issue is that I have a ton of plugins with Logic that it would be a hassle to find the original downloads / serial #'s for. I'm getting rid of the old Mac once everything is transferred so it's okay then if the backup won't work anymore for the older one.

The most trouble free way to move to a new machine,  is using the Setup Assistant on the initial boot of a brand new machine— you have one shot here. https://support.apple.com/en-us/HT205749

The second best way is use the Migration Assistant.

How to move your content to a new Mac https://support.apple.com/en-us/HT204350