Why not use an adapter to make your hdd external via USB, freeing up an internal slot on your PC?

If you have a spare pcie slot you can get a m.2 adapter and a nvme drive, or if your motherboard has a m.2 slot that would be the way to go. I got rid of all my sata and got a 2tb nvme drive and it has been good for a few years and probably good enough for a several more

i just got rid of all HD in my rig. usb 3 is okayish but nothing like internal obviously. I just waited for good sales on ssd's now im all 4tb ssds so should be good for a while

You could get an internal SSD and put the existing HDD into a USB enclosure

My case layout does not allow for any more internal drives, so either I throw away the hdd and buy internal ssd or go for external.

You can move an existing drive, if you want to keep it. Get an external USB enclosure. Get a new, large, SSD. Move the internal drive that you want to keep to the external enclosure. Put the new, large, SSD in its place internally.

I would consider an enclosure with a fan. There's not a lot of airflow in a lot of enclosures.

I have 2 SATA SSDs I use via an USB adapter externally and have never had an issue.

Technically SATA is faster at 6 gigabyte compared to USB 3.0 at 5 gigabyte. That being said USB 3.1 or newer is faster than SATA.

How if we're talking nvme, internal drives are basically always going to be faster than a USB adapter.

does your motherboard have any m.2 slots? if so you could instal an NVMe ssd. if you don’t already know, type “sysinfo” into your task bar search field and see what it says your mobo is then lookup the user manual to see the board layout.

to the question of external drives, id sooner just replace the HDD with a (larger) ssd than go external. also if your case has bays for 5 1/2 inch devices (like an optical drive) they make adaptors to hold HDDs and SSD in those spaces.