I never had this issue since I use GIMP decades ago. But I know in older GIMP versions (and I mean up to relatively recent versions) loading can take very long if you have ton of fonts. I don’t know how long it has been since you tried it out. There was attempts to asynchronously load fonts and other optimizations to make it start up fast. At least for me GIMP starts… let me test it again… in less than a second. Having a fast drive plays definitely a role here too.

And it depends what method you used to install. If it was Snap on Ubuntu in example, well that is on Snap most probably.