God no, don't use Raspberry Pis for media playback. They're fucking dogshit. The chipset lacks hardware decoding for most (if not all) common codecs. Even the 5 is hot garbage for most media purposes. They're fine for the things they're well-suited at (though there are still cheaper options given their weaknesses), but media is not one of them.
Unironically, get an Onn 4K Plus ($30-$50). I know you said you don't need 4K, but it's a lot of horsepower for the price. If you really don't care about 4K and "cheap" is the order of the day, the Onn "Full HD Streaming Device" (aka their 1080p stick) is $15-$30, often going on sale for $14.88 on sale or when logged in to Walmart.com (Onn is a Walmart brand).
They're running plain Android, are Play Store "certified", support sideloading natively, can run Kodi/Jellyfin, and even the shittiest model (the 1080p stick) can reliably play 1080p 60FPS video via Wifi. They're well supported with updates, support the usual streaming apps, but also run the "home media" sidecar stack just fine too. You don't even have to root them to replace the default launcher (which gets rid of the only ads the devices display). Projectivy is the current darling of the custom launcher world.
Avoid Amazon Fire TV like the fucking plague. They aren't even Android anymore; they've baked up their own shitty clone that can't run Android apps and won't allow sideloading. And they've been slowly clamping down on the older models' willingness to run sideloaded apps with functionality disappearing after updates. I used to swear by the Fire TV Sticks ... but Amazon can't abide even a moment going by without a storefront or sales opportunity being shoved in the user's face, so they're clamping down and ruining a good thing. Dumb fucks.