Do you see any red lights with this product?
https://www.amazon.com/gp/product/B07VP37KMB/ref=ox_sc_act_title_1?smid=A28K0QBH3Z1QKZ&psc=1
I have used that ViewHD splitter and its a great product with limitations. I purchased one for stripping the HDCP copy protection from the hdmi output of my Satellite STB but that is not necessary if you're then planning to convert the splitter's hdmi output to a component input. The main drawback is that it's not rated to work with a 4k HDMI input.
I have not found an elegant all-in-one solution but I can vouch for the following products...
HDMI Splitters
https://www.amazon.com/dp/B07VP37KMB/ref=syn_sd_onsite_desktop_137?ie=UTF8&psc=1&pd_rd_plhdr=t
https://www.amazon.com/gofanco-Prophecy-Splitter-Compact-Intelligent/dp/B07GDV1RH2/ref=sr_1_14?crid=204XW347YK3YV&keywords=gofanco+hdmi+splitter&qid=1671177128&sprefix=gofanco+hdmi+splitter%2Caps%2C342&sr=8-14
Importantly, both of these splitters will downscale a 4k 60Hz 4:4:4 signal to 1080p on the 2nd hdmi output (for your Slinbox) whilst allowing you to still enjoy a 4k signal from the other output (for your TV). They also have a micro USB power input so you can use a phone charger as a power source. If your TV box has a USB port you may be able to plug the cable into that for power.
HDMI to Component converter with scaler function
https://www.amazon.com/dp/B083ZF5BBP/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B083ZF5BBP&pd_rd_w=9Qnu8&content-id=amzn1.sym.dd2c6db7-6626-466d-bf04-9570e69a7df0&pf_rd_p=dd2c6db7-6626-466d-bf04-9570e69a7df0&pf_rd_r=NVQ49ATXQTZEZN7B3VRQ&pd_rd_wg=B0Pi0&pd_rd_r=5daae320-77eb-4b76-8fb6-21160de62b9c&s=electronics&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWM&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyN1YzQU5DU1FKRktaJmVuY3J5cHRlZElkPUEwMjkyMzE2SEU5QjMzWE1VQ1BLJmVuY3J5cHRlZEFkSWQ9QTA3MzQyMTlQRDBIV1E4WjNMUjgmd2lkZ2V0TmFtZT1zcF9kZXRhaWxfdGhlbWF0aWMmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl
HDMI to component scalers can be hit and miss. You are converting a digital signal to an analogue signal. Avoid "passive" converters (these are usually unpowered - replying only on the power provided by the HDMI input) as I've found them to be unreliable.
Read up on EDID management and read the instructions that come with the HDMI splitter that you purchase. You'll need to set the dip switches on the above HDMI splitters to get the HDMI signals right. If you purchase a splitter with no EDID management you may have problems splitting a 4k signal to a mixed 4k / 1080p output.
As with everything, you generally get what you pay for. Cheaper options are available but you should expect mixed results.
Tried this 4K HDMI Splitter 1x2 HDR D-o-l-b-y Vision Atmos i hope resolve your problem.
i used fire tv 4k max & NVidia Shield (old version) & vizio m512a-h6
1 Input to 2 Output
2 Input to 2 Output
BTW , you can shorten your amazon links by chopping them off after their product id. Like below.
Now will this add any input or response time lag?
https://www.amazon.com/dp/B07VP37KMB/ref=cm_sw_r_cp_api_glc_fabc_aHH6Fb31QPD1N
This the same one you had? Just tried to find it on the us amazon store but it looks the same
Do you see any red lights with this product?
https://www.amazon.com/gp/product/B07VP37KMB/ref=ox_sc_act_title_1?smid=A28K0QBH3Z1QKZ&psc=1