My Acer Aspire 3 has Radeon Vega 8 and Radeon 540X in it, but lately the dedicated card kept disconnecting. I've seen many posts, that I should uninstall it in device manager. I did it and then used utility tool to get rid off all drivers. I've downloaded the latest adrenalin software but it can't see my 540X and just updates Vega. How can I make my dedicated card visible by system again?
I would open a Acer Support Warranty ticket to have Acer check your laptop GPU card to see if it is defective or the motherboard is defective or everything checks good.
But if your laptop is older than a year old then most likely the Warranty has expired according to Acer Warranty: https://www.acer.com/ac/en/US/content/standard-warranty
You can try and contact Acer Support and see how much they will charge to check your laptop when not under Warranty from here: https://www.acer.com/ac/en/US/content/service-contact
Note: by your description it sounds more like a hardware issue rather than a software issue.
Already had it on warranty for broken cooling fan about half a year ago or so. I think that I have 2 year warranty so I will make new ticket on acer support
According to Acer your laptop has a one year Warranty on it unless it was purchased before 2019.
Anyways, it is possible when Acer repaired your laptop they may have loosened up or did something to GPU card on the motherboard.
Need to find out if Acer Warranty Repairs has a Warranty period on it if your original Warranty has expired.
See if your Acer laptop has its own Diagnostic Software to check your laptop's hardware and software. If it does run it and see what comes up if anything.
Found this at Acer about diagnostics: https://www.acer.com/ac/en/US/content/software-acer-care-center