Must replace laptop, are there any HP laptops to avoid, I use Ubuntu 18.04 lts, and Mint 18.3.
Avoid because of what? Every Laptop on earth has its downsides, no matter how expensive or good…
I haven’t heard of any to be honest and since HP printers work well with Mint and as far as I know Ubuntu as well I don’t think there will be any. You might consider updating to Mint 19 just to make sure which you can do through 18.3 or as a clean install: these are the only things I have come across https://forums.linuxmint.com/viewtopic.php?t=275326 but there is a good HP Site https://h30434.www3.hp.com/t5/Notebook-Operating-System-and-Recovery/Problem-installing-Linux-Mint-on-m2y49ea-acb-laptop/td-p/6589160 which you may care to look at first
By to avoid, I mean are there any models which are known to be difficult or impossible to install and run these Linux distributions on, Thanks.
This depends on your budget versus your specification expectations, and where you source a laptop.
I’ll assume you do not want to repair or rebuild a laptop to suit your needs. Reputable dealers, cost a premium, compared to the same model of laptop brought via ebay, for half the dealers price. Its shop Warranty versus eBay return policy if the machine doesn’t work on arrival or dies within 14 days.
High end machines cost more and tend to have longer serviceable life (better warranty) than budget low cost and spec machines.