"won't be used for watching TV channels. "
"It needs to act as a computer"
"wireless keyboard and mouse"
unless you describe better the intended use and reason for the constraints, it will be difficult to provide you with better ideas.
the best I could summarize your requirement would be "screen/monitor that integrates a computer" in one piece.
the device coming closest to your requirement would be an apple imac, except for the price.
insisting on a one-piece device does not make economical or technical sense (think about codec* updates, parts failing, ease of upgrade, etc. ), unless there are "reasons" you might want to explain.
* regarding codec updates, already H265 (or VP9 in apple tech) requires a fair amount of computing power to decode the high compression, that's why you won't find any very cheap screen device doing it. Devices that do it, will typically offer smart-TV functions, but IMO it's a waste to put such a processor in a TV/screen. And I expect that non-computer devices currently supporting H265/VP9 will not be able to be upgraded to support whatever next compression standard that will be released due to insufficient computing power.
if you give up the "one piece" requirement, the best solution would be an android streaming box + a cheap screen.
and oh yeah, I had horrendous experience with TCL brand, both the quality of the product and their warranty/support service. never again.