In the times when Windows 2000/Millenium was something "new" i played an 2D platform game, where we play as a dog(?) and we need to rescue animals (collect them, when player "pick up" them, they follow player to the end of the level, when player jump, they jump too in the same place, like for example to jump over obstacle/hole, they follow like a snake : )), we also collect fruits(?) to get points, hearts and clocks (you could die from not finish the level in time) and had to watch for traps like spikes(?) etc., there were also enemies but it was almost 20 years ago so don't remember if there was even music, maybe WinXP was avalible on the market but wasn't popular at this time yet. It was nice pixel platform game with animals.
Please, help.

Might be a stretch, but maybe Flicky? Although it was a Genesis game, and I don't think it was ever released on PC.
Video of the game: https://youtu.be/kWVGrqRdjDs

(also sorry for the necro)

Apparently Flicky was originally an arcade coin op game. According to Mobygames it was released also to Windows, but that was as late as 2010, apparently the emulated Genesis version.

https://www.mobygames.com/game/flicky
https://store.steampowered.com/app/71111/Flicky/

So if it was that game, maybe he was playing it on PC on either MAME or a Sega Genesis emulator...?

some aspects of the game sound like something I should know but the game is likely before my time so sadly idk...

I can think of Offspring Fling, but that's probably more recent than tc is thinking of.

Description didn't remind me of anything but _Auster_ post helped me remember since gameplay loop seems to be same.
The game is called Happyland Adventures and it's fun little platformer with memorable main theme. It was freeware game and it also had Xmas Edition if you feel like revisiting it.

I always get that and Wonderland Adventures confused (3D children indies games from mid 2000s)

Well I wouldn't necessarily call them children games but yeah, freeware games were quite popular back then and a lot of them were quite similar. I wonder do today's kids play them like we used to?
EDIT: Scratch that last, today's kids don't know anything beyond Tik-Tok.

Didn't know about replies for this thread, but yes, it was Happyland Adventures, thx.