If you went with the one time purchase of version 2.0 in March 2023, there won't be any upgrades for you since that license is locked to version 2.0. To upgrade to the new version requires purchase of the Upgrade Pass. So maybe the $0.99/month subscription plan may be worth it after all.
Clip Studio Paint is having their 2023 summer sale now and there are some good discounts.
The one time purchase of version 2.0 of CSP Pro and CSP EX desktop licenses are US $19.99 (60% off) and $129 (40% off) respectively. Getting the full version of CSP (non subscription) for $20 is an amazing deal.
If you don't mind subscription, the 1 year subscription (single device) for CSP Pro and CSP EX are US $9.99 and $34.99 respectively. That is also a pretty good deal.
You can see all the other products on offer via this image link below: