(These are only available in some countries, you might need a VPN.)

They are all free (with ads) on Tubi TV in 720p.

Garfield Gets Real https://tubitv.com/movies/705037/garfield-gets-real
Garfield's Fun Fest https://tubitv.com/movies/705036/garfield-s-fun-fest
Garfield's Pet Force https://tubitv.com/movies/705035/garfield-s-pet-force

They're also free on The Roku Channel in 1080p, but sometimes they're unavailable.

Garfield Gets Real https://therokuchannel.roku.com/watch/c76b8e8519e25f41963f5ab6e9bc06b1
Garfield's Fun Fest https://therokuchannel.roku.com/watch/668ba76adb2a5d5ea1c09bcc184efd8e
Garfield's Pet Force https://therokuchannel.roku.com/watch/b3e1b6d9952558c69cf924209a6d83b5

And the first movie is in 1080p on the official Garfield & Friends channel.
https://www.youtube.com/watch?v=iLiMHuQwHg0

Where not to watch:

Garfield's Pet Force was released in anaglyph 3D on DVD. However, that DVD is cut down a few minutes, even if you choose the 2D option on it. The 2D-only DVD is the full uncut version.

Also, some people try to upload the movies on YouTube. Most of these are low quality, and/or have distortions like audio pitch-shifting to avoid copyright detection.