Is it disabled? Do you have some css or js code that might have somehow affected that element?
It doesn't allow TValue to be as string , it throws error cannot implicitly convert from Ienumberable to string . I tried giving TValue to IEnumerble it still didn't allow me to search .
Yes, that was stupid on my part. I edited my question 
I am able to select the things from the dropdown but for me to search it dont allow me to type anything there . I don't have any css or js for this element .
Do you at least have the pointer blinking (like you will start writing), when you click on it?
Nope i click there and it does nothing. it behaves like search don't even exists although i see the little search icon.
As if it's disabled. Have you inspected that input element in this situation? Something wrong there?
looks like below
input id="search3OuI30m96E" tabindex="0" class="rz-inputtext" role="textbox" type="text" onclick="Radzen.preventDefaultAndStopPropagation(event)" _bl_485944e5-3b4c-423f-b671-b425877d3149=""
and for the radzendrop down which don't have multiselt=true . looks like below
input id="search3gKRESN-ak" tabindex="0" class="rz-dropdown-filter rz-inputtext " autocomplete="off" type="text" _bl_87cdbc7f-3569-4af7-bf94-5ce681fdbdfd=""
both of them acts like as if it is disabled.
In browser devtools give that input css rule: z-index: 1000 (some number). I wonder if that will "unlock" the writing.
Nope, it didn't i kind of stuck with this problem from last 3 days and i can't understand why
Me neither. Is it the same on different browsers?
yes its same on all the browsers
If you try without that class (looks like a bootstrap thing) ?
Nope didn't it help though.
I found something interesting . I added a new radzen dropdown for the page which is not a modal popup ,it works fine but if i do the same thing in the modal popup page it doesn't work . same exact code.
Alright i fixed it basically i am opening Modal by saying Model.Show for some reason if i use this to open modal , dropdowns search wont work so i used DialogService,OpenModelAsync and now dropdown search works. lol .
For anyone else, I had the same experience with the dropdown search/filtering not working in Bootstrap modal (Bootstrap v4.4). I ended up just using the multi-select listbox https://blazor.radzen.com/listbox in the Bootstrap modal and that worked. It doesn't give the same dropdown selection experience but I can at least search and select items in a list.
But it sounds like using the Radzen DialogService https://blazor.radzen.com/dialog modal to display the dropdown instead of Bootstraps modal would work as well, just haven't tried that.